Use of Zonisamide for Cats

Use of Zonisamide in Cats

Zonisamide has been recommended for use in cats and dogs with seizures for almost 20 years despite a lack of efficacy studies. Not that this is surprising -we love to extrapolate from human and canine medicine to cats – but it was frustrating to say the least. Well, that has been improved recently after a study evaluating the effectiveness of add-on zonisamide OR single agent zonisamide in a population of cats with seizures. (https://doi.org/10.1111/jvim.16984). This was a retrospective study of 57 cats, with seizures of any etiology that were prescribed zonisamide as part of their treatment plan. Of this group, 16/57 were diagnosed with idiopathic epilepsy (Tier II level confidence), 4/57 neoplasia, 4/57 had congenital brain disease, 2/57 head trauma and 1/57 with metabolic encephalopathy. The remainder (30 cats) did not under go diagnostic testing to obtain a diagnosis and were treated for presumptive disease based on the clinician’s assessment.

Results

Prior to treatment, the majority of cats were reported to have generalized seizures with both focal and generalized seizures taking second place. Focal only seizures were a distant third place with only 12 cats. The cats in this study demonstrated a significant reduction in seizure days (number of days having a seizure) and seizures (total count) per month following administration of zonisamide. Within the confirmed idiopathic epilepsy group, this group had a reduction in seizures/month of 1, with a total of 69.2% of cats with idiopathic epilepsy responding to zonisamide treatment. This equates to 9 of 13 cats for whom they had efficacy data. Add-on zonisamide was noted in 33 cats for whom 56% responded to treatment. Lastly, for cats whom zonisamide was the only AED, a 70% response rate was noted. A few cats had an increase in seizures after starting zonisamide. This may have been related to disease progression or resistant epilepsy. The retrospective nature, along with the lack of diagnostic testing in all cats, makes assumptions difficult.

The median daily dose of zonisamide was 7.55 mg/kg (range 3.8-17.7 mg/kg) and it was given q12h most commonly (36/57 cats). This drug can be given q12 or q24h based on the PK available.

Adverse effects were noted in 15/57 (26%) which is relatively low compared to the reported adverse effects for, say, phenobarbital. The adverse effects included inappetence (n=10), transient sedation (n=6), ataxia (n=4), vomiting (n=3). The adverse effects appeared dose related therefore higher doses resulted in more frequent adverse effects. The adverse effects lasted for variable amounts of time but typically 2-4 weeks. Mild changes to CBC were noted but significance was unknown due to concurrent disease. Liver enzyme elevation including ALT, ALP and ASK was noted but increases were mild.

What’s the take home message?
Zonisamide appears to control 56- 70% of seizures for cats, regardless of etiology. This number is closer to 70% for idiopathic epileptic cats.
Zonisamide has a low incidence of adverse effects, however the nausea/vomiting/anorexia adverse effects should be closely monitored.
Zonisamide is metabolized through the liver and is a sulfa derivative so use caution in patients with a known sensitivity.
 
I hope you enjoyed this week’s TidBit and will join me in celebrating the publication of solid data about zonisamide! I hope you have a great week and look forward to working with you soon.

Neurodisability Score for MUO

As discussed last week, a neurodisability score (NDS) has been proposed for use in dogs with meningitis of unknown origin (MUO). The goal is to help grade the clinical signs more objectively and, hopefully, prognosticate more accurately. The score was developed by Drs. Goncalves et al (https://doi.org/10.1111/jvim.16717) from the UK and published in 2023.

A retrospective evaluation of medical records was performed to identify common clinical signs at presentation. Subsequently these signs were grouped in to the following categories for prospective use: seizure activity, ambulatory status, posture and cerebral, cerebellar, brainstem and visual signs. For the prospective part, the score was tested on 31 dogs diagnosed with MUO. Table 2 of the published article has an outline of the scoring system which I would suggest you look at if you have time. As an example, under the “ambulatory status” section the options are “normal, mild paresis or ataxia but ambulatory without falling, moderate/severe paresis or ataxia with frequent falling, and nonambulatory”. Each of these options is given a numeric score from 0 (least severe) to 3 (most severe). As the categories are worked through, points will be accrued based on their neurologic exam. The maximal score is 21, indicating he most severe disease. According to the article, the mean score at presentation was 8 +/- 2.85 points. All of the things that you imagine would affect this score such as concurrent disease, treatment prior to referral, and evaluator skill must be considered here (which the authors did consider, for the most part). In the end, they found a significant difference in dogs that survived to discharge (median 8; range 3-14) and those that did not (median 12.3; range 8-13). You can see as well as I can that there is marked overlap between the ranges which makes it difficult in a clinical patient to draw conclusions. Furthermore, the study did not evaluate validity (did the test measure what it was supposed to be measuring) and did not find an association at a specific cut-off value related to long-term outcome. The study presented in last weeks TidBit Tuesday suggested a cut off value of 7 would be used to predict death by 6 months for dogs with MUO. I’m ecstatic that this work is being done but caution you to use it with care. Euthanizing a pet simply based on this score feels inappropriate at this time. Predicting a poorer possible outcome at 6 months and relaying this information to a client would be an appropriate use of the NDS. It IS encouraging that we may have a universally available tool for ALL VETS (i.e. not a specialty tool like an MRI, or a neurofilament in CSF) that we can use to talk about MUO in objective terms. As with most of the TidBit Tuesdays there will be much more to come on this topic over time so stay tuned!
 
Thanks for reading! Changes to my schedule are once again upon us as the summer sets in. My schedule varies WEEKLY so please reach out if you have a case that needs to be seen but cannot find a suitable time on the schedule; I may have more flexibility than what is listed, so please ask. I will be closed at the end of June for a few days for a family wedding, and mid-July for the Dane County Fair but otherwise anticipate high availability for you this summer. Enjoy the beautiful spring weather and the delicious smells of blooming things this week!

The Prognosis Meningoencephalitis of Unknown Origin

Meningoencephalitis of unknown origin (MUO) is a frequent diagnosis for dogs with multifocal neurologic signs. The name should tip you off that we’re still figuring out this interesting disease amd do not know the underlying cause yet.  It is thought to be immune mediated, and therefore treatment often includes an immunosuppressive dose of steroids +/- an additional immunosuppressive such as cytarabine, azathioprine or cyclosporine. Despite decades of awareness of this disease we are still working out the prognostic indicators. Back in my academic days, a resident of mine and I tried to sort out this question by evaluating brain MRI results, with little success. A recent study took another crack at the elusive prognostic indicators and published their findings in JVIM (Goncalves R, et al. JVIM 2024).

Materials and Methods

447 dogs were included in this retrospective study from 2 institutions. Did you see that giant number of included cases?? Go vet med, go! Anyhoo, the authors included dogs with signs of inflammation (brain MRI, spinal tap) and because it was a retrospective study, there were a number of different treatment protocols included. Perhaps this creates too much variability to carefully evaluate outcome or prognosis. I might argue that  there is no other way to accrue a large number of cases of MUO. A neuro disability score (NDS) was assigned to these patients (score developed by the author and several others and published in 2023). Survival was reported.

Results

I’m going to list some of the key results below but if you wish to learn more about the results, please refer to the article. It is well written and comprehensive.

• Median age at presentation was 48 months

• 
  The majority of breeds represented were small breeds, but a few Labs, spaniels, and larger dogs were also included.

• 
  The season of diagnosis was equal across all 4 seasons

• 
  Common presenting complaints were proprioceptive deficits (77%), ataxia (65%), obtunded mentation (62%), seizures (32%).

• 
  The most common neuroanatomic lesion localization was multifocal (43%), followed by forebrain (29%)

• 
  Median follow-up time was 11 months. 82% of dogs survived to discharge and 63% were alive at 6 months.

• 
  A significant difference in survival was noted for dogs WITH a NDS compared to those without and a score of greater than 7 resulted in a sensitivity of 61% and specificity of 67% for predicting death at 6 months after diagnosis.

• 
  Relapse occurred in 50% of dogs that survived to discharge

• 
  Of those that relapsed, incomplete resolution of neurologic disease during the 6 month follow-up period, a higher NDS and neurologic signs >7 days duration before intervention were statistically associated with relapse.

What should we do with this information?

The take home message should be that we should perform a NDS on patients with suspected or confirmed MUO to help provide a prognosis AND that a more rapid referral may provide a better long-term outcome.

Stay tuned next week for a review of the NDS! Thanks for reading and I Hope you have a great rest of your week!

How Well Do We Communicate?

How Do We Communicate?

An article recently came across my desk that I found enlightening and hope you will too. The topic today is about communication, specifically, communication with owners and vets about neurology. I find myself using a LOT of words in my consultations with owners and often wonder if those words are having an effect. You are not alone if you find neurology daunting – many clinicians do – and that innate worry can lead to communication barriers, too!  Prior to COVID I used a white board and wrote key points on the board as I spoke to owners. The COVID pandemic resulted in a large percentage of telephone based conversations and the white board wasn’t there. Now that I’m back to in person consulting, the white board is back too and I think, highly subjectively, that I see a difference in client comprehension. That is why this article sparked my attention. I am always trying to figure out ways to communicate as effectively as possible with you, my actual client, and your client (aka the pet’s owner) so that the pet gets optimal care.
The article I’m referencing is by Dr. Thomas Flegel (a German neurologist) and his colleagues (JVIM 2024 1-4). In this article Dr. Flegel and his team evaluated the client’s recall of the discharge and compared that to the clinician’s recall of the discharge. There were 3 parts of the study. Part 1 and 2 were only answered by the client and they pertained to demographic questions of the owner and atmosphere/comfort level during discharge. Part 3 was about the diagnosis, treatment, and long-term plan. A raw percent agreement was then calculated for different questions. Part 3 was repeated 2 weeks later.

Results

I had preconceived ideas that age, maybe native language speaking and level of education would influence these results. I was wrong! The only statistically significant difference was the client’s age; increasing age lead to a decreased raw percent agreement. This meant that clients over 50 years old had a more difficult time recalling the specifics about the case compared to the clinician. I don’t believe they accounted for clinician age in the study, but they did evaluate clinician experience.

The three questions that had significantly lower raw percent agreement 2 weeks later. Those questions were
“Should you give the medication before feeding your pet?”
“What are potential adverse effects of the medicine you have to give your pet?”
“If your pet has to live permanently with signs of the disease, which are those?”

Their conclusion was that we should emphasize the most important parts of a pet’s medical care when we discharge them (or finish a consult, in my case). The researchers also commented that many clients could refer to the discharge instructions to answer the questions therefore resulting in similar answers but their response was “who cares?” In a practical sense, if the client wants to remember the side effects of the medication, for example, we HOPE they will refer to the discharge paperwork!

After each consult I summarize the findings for both the attending clinician (you) and the client. I know many of you write summaries for your clients as well. Some parts of my written summaries will be over the heads of some owners because it is intended for you (my client) and some of the discharge will be too simple for you because it is intended for the client. But having all the information available to all parties can only improve understanding and follow through. Hopefully this limits the number of clients coming back to you with questions after my consult, and I have been told it helps many of you recall my BILLIONS of words when the client calls with questions. I know they’re long but hopefully they’re not unapproachably long. If you have a suggested change to the summary forms, I’d really love to hear from you!
 

Thanks for including me in your patients’ care. I look forward to working with you (and writing down my findings) soon!

Sciatic Nerve Injury in Dogs and Cats

Dogs and cats commonly present for brachial plexus injury, usually after a trauma, but what about sciatic nerve injury? The sciatic nerve is composed of the peroneal and tibial nerves and makes up a lot of the L6-S3 nerve roots. It's a big one! So, how easy is it to damage all or part of this workhorse? Damage can take on 3 forms. First, and most severe, is neurotmesis which means transection of axion and myelin and perineural tissues. Second, is axonotmesis, which suggests damage to the axon with preservation of the myelin and perineural structures. Finally, and least concerning, is neurapraxia, which results in functional damage but minimal to no structural damage. Neurapraxia could be like a "stretch" or loss of minimal myelin. A recent study, published by Dell'Apa, et al from Italy, outlined the signs, etiology and prognosis for 38 dogs and 10 cats diagnosed with a sciatic nerve injury. 

What are common clinical signs of sciatic nerve injury?

According to their study, Dell'Apa et al found that the majority of dogs (~80%) had either a loss of hock flexion, or a lack of hock extension. Along with this, about 75% of dogs had a loss of proprioception in the affected limb. There was variable sensory loss (deep pain) and about 13% of dogs had evidence of a root signature. All cats demonstrated a loss of hock extension (i.e. showed dropped hock) and 90% showed a loss of hock flexion. No cat showed signs of a root signature and only 5 cats (50%) showed changes in sensory. Remember, these cases are MONOparesis or plegia! No paraplegia/paresis would be expected for this disease. 

Which nerve was commonly affected?
Tibial nerve: dogs - 16%; cats 20%
Peroneal nerve: dogs - 37%, cats - 60%
Sciatic nerve (common trunk): dogs - 47%, cats - 20%

What are the most common etiology?

The most common cause of sciatic nerve injury in dogs was bite wounds (24%) followed by surgery (TPLO, TPO, DPO, Modified retinacular imbrication, or removal of an intramedullary pin; 18%), and then trauma. I must add here that the bite wounds were caused by wild board. Wild boar! It's Italy, remember? The most common cause of sciatic nerve injury in cats was pelvic trauma (50%), followed in equal amounts by surgery for a femoral fracture (20%), and an IM injection (20%). Only 1 cat sustained a bite, and it was from a dog. Apparently, cat's aren't tasty to wild boar. Or they're faster. (Or not used for hunting wild boar??)

What was the outcome?

A poor prognosis was deemed one that resulted in euthanasia, arthrodesis of the joint or amputation of the limb due to poor function. A good prognosis did not necessarily mean a return to normal, but instead indicated limb function had improved. Animals that were able to flex and extend their tarsus had a significantly better long-term prognosis than those that couldn't. Furthermore, loss of deep pain was NOT a prognostic indicator in this study. This is different than spinal cord studies in which the loss of deep pain is a strong prognostic indicator. Peripheral nerves can regenerate and therefore this loss wasn't useful for predicting recovery. Overall, 9 of 32 dogs (28%) and 1 of 9 cats had a negative outcome. This suggests a favorable long-term outcome for this population of animals. 
 
Thanks for reading! A quick reminder that I am away until Thursday (May 9) so you may experience a delayed response to emails, texts or phone calls. Happy Mother's Day to all who celebrate! 

Neuroanatomic Lesion Localization Practice Case

It's time to sharpen those pencils and put on your thinking hat. It's neuroanatomic lesion localization practice case time! 
Signalment: A 4 year old FS Mixed breed dog (along the lines of a Pitbull X)
History: The patient presented with a 24 hour history of acute onset ataxia, and weakness. The owner's noticed significant muscle fasciculations in the neck (mistaken for seizures) along with a reluctance to lift her head. The weakness was progressive from thoracic limb lameness initially, through ataxia to ambulatory tetraparesis. No medications had been given prior to the consultation. 
PE: Unremarkable other than BCS 7/9
Neurologic Examination
Mentation: QAR. Friendly, but subdued.
Cranial nerves: Normal
Gait: Ambulatory tetraparesis, worse on the left thoracic leg. She was noted to have reduced mobility in the left thoracic limb along with a lack of adequate weight-bearing on that limb. The other three limbs were weak, but she could bear weight.
Reflexes: Absent withdrawal left thoracic limb. Normal withdrawal noted in the other three limbs. Normal patellar reflexes bilaterally. Normal anal tone and perineal reflex along with c. trunci reflex. 
Postural reactions: Absent paw replacement testing all four limbs.
Palpation: Painful with cervical palpation and unable to perform cervical ROM without yelping. 

Neuroanatomic lesion localization: where should we start?

The easiest place to start is with elimination.
A. We do NOT have a seizure history, change in mentation or any cranial nerve deficits, right? The lesion therefore is unlikely to be rostral to the foramen magnum. 
B. We have evidence of disease in all four limbs therefore the lesion must be cranial to the T3 spinal cord segment. (If the lesion were caudal to T3, we would expect the thoracic limbs to be normal and without deficits.)
Okay, so far, we have now narrowed our findings to C1-T2
C. The reflex arc is C6-T2 in the thoracic limb. Do we have any evidence of reduced or absent thoracic limb reflexes? Yes - the left thoracic limb has a reduced withdrawal reflex. Animals with reduced reflexes have their lesions IN the reflex arc (C5-T2 or L4-S3 in the pelvic limb). 

Lesion localization is: C6-T2 spinal cord, more affecting the left side

What would you consider for differential diagnoses? 

In this case, the two most important historical factors that I would focus on are the "acute onset" and "painful" parts. Things like neurodegenerative disease are not painful, and rarely acute. The most common painful myelopathies I like to summarize as being "2-Ds, 2-T or an M". What are they? Disc herniation, discospondylitis, tumor (I know, I know, it's called neoplasia but it's easier to remember 2D,2T,M.), trauma and meningitis/meningomyelitis. 

Because this isn't a disease-focused TidBit I'll cut to the chase and tell you that this dog was diagnosed with a type I disc herniation and had surgical decompression. She felt much better! 

How did you do? Did you enjoy this case this week? Sometimes the simple ones are the hardest because we over think them so much! If this wasn't a simple one remember that I'm available to help you with cases. Neurologic cases aren't fun for everyone so reach out for help if you're stuck! 

Thanks for reading. I will be away at a conference and taking a little vacation time May 4-8th. I will have some access to email but please be patient with inevitable delays. Thanks for including me in your patient's care! Have a great week and stay safe.

Is there a Weekend Effect in Veterinary Medicine?

The “weekend effect” (WE) is a term used to describe poorer patient outcomes associated with treatment out-of-hours. There has been debate in the human literature if this effect is “real” or not. Specific focus has been aimed at mortality or morbidity associated with the WE. A recent study in England, looked at the WE in relation to decompressive hemilaminectomy surgery in a cohort study (comparing a poputation of dogs having surgery afterhours to those operated during business hours) and, I found it informative. (Low D, et al. Veterinary Surgery. 2024;1–10.)

You may be aware that the timing of spinal cord decompression has been hotly debated over the past…oh..100 years or so. Recently, some studies have suggested that surgical decompression for an acutely non-ambulatory dog is not an emergency and therefore can occur during normal business hours. This has been suggested for dogs with and without deep pain sensation. Additional studies have supported that in fact it DOES matter and those studies advocate for decompression of dogs with a loss of deep pain within 24 hours of documented loss of deep pain. I tend to favor the “don’t wait, cut ASAP” approach but the choice is controversial. The study by Low and colleagues from England did not address the pros or cons of timing of surgery but instead looked at outcome (did they walk, or not) and adverse events (urinary tract infections, gastric ulcers, skin infections/ulcers, post operative neurologic deterioration, etc.) for dogs undergoing back surgery within or outside of business hours.

The findings of this study were interesting. They identified a significant difference in postoperative morbidity and the recovery of ambulation in a group of dogs undergoing surgery afterhours vs those undergoing surgery during business hours. They stated that 1 in 8 dogs would not recovery ambulation when exposed to weekend surgery compared to if they were exposed to weekday surgery. Furthermore 1 in 7 dogs would experience an additional post operative morbidity when exposed to weekend surgery, compared to weekday surgery.

What contributed to the results? The variables for a patient undergoing, and recovering from, surgery are numerous regardless of the timing of the surgery. For example, there are pre-hospital variables (such as the timing and treatment provided by the referring vet), hospital variables (staff tiredness, case load, surgeon experience) and post-hospital factors (availability of aftercare support in the patient’s home, the hospital discharge process). Many of the hospital variables were evaluated in the study and not statistically associated with outcome or morbidity. The pre- and post-hospital factors are more difficult to study due to the inherently heterogenous state.

What do I do with this information? I included this study as at TidBit Tuesday to increase awareness of the possible WE in both veterinary medicine at large (yet to be fully determined) and specifically within neurosurgery. The data does not suggest that you shouldn’t make a referral if you have a nonambulatory patient, especially if they’ve lost deep pain! It also shouldn’t be used to deter a client from pursuing surgery on a weekend or afterhours. I’m not sure there is an actionable outcome by gaining this knowledge, except for the simple purpose of increasing your (and my) knowledge of the existence of a WE. By being aware, we can sometimes change our actions in subtle ways that may improve the outcome for our patients. Have you ever managed an especially difficult seizure patient? What if you had a dog develop liver disease while taking zonisamide or phenobarbital? Those cases increase our awareness of the “bad” outcomes and increase our sensitivity to treating the next seizure case, or next dog on zonisamide or phenobarbital. In fact, population statistics would suggest that a low number of dogs have resistant epilepsy but when it is 1 of your 10 or so cases that you’ve managed it feels like a high risk and may change how you discuss seizures with the next client that walks in the door with a pet with seizures. Awareness of the WE may change how we, as neurologists, operate and intern may affect the WE. Time shall tell!

Thanks for reading through this long TidBit. I hope you enjoyed the lovely weekend weather (it was in the 70s for us!) and have a wonderful week.

Neuroanatomic Lesion Localization for Busy Vets

What is the neuroanatomic lesion localization for the following case?
Signalment: 4 year old FS DSH
History: Acute onset inability to blink one eye. No history of trauma. She is an indoor only cat. 

To answer this question, of course you must start with a cranial nerve exam. At its most basic level, the cranial nerve examination is a process of elimination. Let's start with the blink reflex. If you touch the medial and lateral canthus, what cranial nerves are you testing? (CN 5 and CN 7) How do you know which nerve is affected? To do this, we try to isolate each cranial nerve in the reflex to see which one misbehaves. How can you isolate these two nerves from each other to see which is the affected nerve? Lets's try a corneal reflex! When done correctly, the cotton swab touches the cornea and the eye retracts into the socket. Doing this tests CN 5 (sensory) and 6 (motor). Voila! If the cat does not blink when you touch the medial or lateral canthus, but DOES retract the globe when you do corneal reflex which nerve is affected? Think you know... scroll (or read!) to the bottom to see the answer. 

But wait! That is only part of the question. We have now localized which cranial nerve is affected but we don't know if this is a central or peripheral nerve lesion localization, right? To look at the brainstem we focus on the nerve pathways running towards and from the forebrain and determine if they're affected. The nerve pathways that are easiest to test are proprioception and motor/tone. Watching the animal walk you may be able to detect a toe drag or delayed placement but ultimately we have to test proprioception through paw replacement testing or my personal favoriate for cats: tactile placing. Similarly, when watching the patient walk you may see a hemiparesis (weakness on one half of the body). Often this is more obvious in the pelvic limb but both ipsilateral limbs can be affected. The last piece to the puzzle is an evaluation of level of mentation. If the animal is obtunded, stuperous or in a coma, we have an effect to the brainstem RAS. If you have 1 or more of these signs, the animal has a brainstem disease. If we DON'T have delayed proprioception, evidence of hemiparesis or a change in mentation, we are more likely to be dealing with a peripheral neuropathy.
Remember:
1) cranial nerve deficit + delayed paw replacement/tactile placing, weakness or decreased mentation = brainstem.
2) cranial nerve deficit without the above = peripheral 

Answer: Cranial nerve 7 is affected. (5 is normal in corneal reflex therefore it is not the problem in the blink reflex either.)

Thanks for reading and have a great week! Do you have a case that is puzzling you? Please reach out - I'd love to help. Did you know I also do onsite or virtual private CE for hospitals? Reach out for more details, if you're interested.

Artificial Intelligence in Neurology

Artificial Intelligence (AI) has really taken off in the last few years and, as such, has driven us as veterinarians to critically evaluate where and how we would like to utilize this new technology. Last year I reported to you about a lecture I listened to at ACVIM about the use of AI for writing radiology reports. It was eye opening, to say the least! Recently (October 2023), a group of mostly veterinary neurologists took on AI in a new way. Abani et al challenged 13 boarded neurologists from Europe and North America to distinguish between AI-generated abstracts and human-generated abstracts. The results are chilling...

Materials and Methods

There were 3 test topics provided in this study. The purpose of providing 3 was to discriminate between "highly familiar" topics and the less familiar topics to see if there was a difference in detection of AI by the reviewers. 
Topic 1: SARS-CoV2 scent detection in dogs (considered low familiarity)
Topic 2: Biomarkers for SRMA (considered high familiarity)
Topic 3: Staining of cannabinoid receptor type 1 (medium familiarity)
An abstract, reference and introduction paragraph were written by humans on these 3 topics. ChatGPT was then used to generate 3 additional abstracts, with references and an introduction paragraph on the 3 topics. It was interesting that the authors noted ChatGPT was prompted as such: " Write an academic abstract with a focus on (subject) in the style of (author characteristics such as position, gender and age) at (University name), for publication in (journal name)." I mean...wow. ChatGPT is able to provide gender, age and position sensitivity. 

Results

• Topic 1 and 3: 4/13 (31%) correctly identified the AI generated abstract when only provided the abstract without references and introduction paper. This increased to 9/13 (69%) when all parts were provided. 

• Topic 2: 7/13 (54%) correctly identified the AI-generated abstract (provided alone), which increased to 10/13 (77%) when all parts were provided. 

Two separate plagiarism detectors were studied in this study as well. All of the original published manuscripts were noted to have 58%-100% similarity to available work which indicated this had been published elsewhere (it had). Test 1, 2, and 3 with the AI-generated papers had similarity indexes of 0-18%. This suggests that the plagiarism detectors could identify what had been previously published (the human-generated papers) and which hadn't (the AI-generated papers). Furthermore, they then evaluated all of the abstracts with an AI-detector. All original manuscripts were noted to have 0% AI-writing. Test 2 was noted to have 100% AI generation, and Tests 1 and 3 were noted to have 0% content written by AI. Gulp. 

Where does this leave us? My heightened sense of anxiety about AI-generated content was further heightened when realizing that many of my well respected, high academic achieving colleagues struggled to distinguish between AI-generated abstracts and human-generated abstracts in an area of our specialty. This further reinforced my commitment to reading the entire paper, whenever possible, before considering the data valid. We were taught to do this in school but alas, with our busy schedules, it can be missed. AI is not all bad, however. It can be quite helpful for correcting grammar, editing, summarizing references or papers and even performing statistics. I would encourage all of us to move through published literature with our eyes fully focused and with awareness of the use of AI in modern veterinary medicine. Except yesterday...hopefully you kept your eyes partially closed and didn't look directly at the sun!! 

I hope you enjoyed this little TidBit. It is a little bit off topic, but I hope you will find it useful, nonetheless. Please know that my TidBit Tuesdays are (to date) fully human-generated, as are my patient reports! Let me know if you have any topics that you'd like me to cover. Have a great week!

Vestibular Epilepsy

Wait, what? Did I read that correctly? Yes, you did! What do you call acute onset, transient vestibular signs? Vestibular paroxysmia (VP)! What do you call it if you have interictal spike and wave forms on EEG (which suggest an epileptic focus)? You guessed it... vestibular epilepsy (VE). 

What is Vestibular Epilepsy?

In human neurology, there is a form of epilepsy in which patients have acute onset vestibular signs (drifting, rolling, nystagmus) that seconds to minutes. If the onset is associated with body position change, it is considered a paroxysmia (VP). However, when an EEG is performed, human patients with vestibular epilepsy will show classic changes consistent with seizures in the temporal and parietal lobes. The big differentiator between paroxysmia and epilepsy is the response to treatment and the presence of changes on EEG. In veterinary patients there are very few studies evaluating this form of epilepsy but clinically perhaps some of you can think of a patient (or two) with similar clinical signs? We see this, albeit rarely!

How To Diagnose Vestibular Epilepsy

Diagnosing VE in veterinary medicine can be challenging. Patients will present with repeated, transient vestibular signs and are normal on examination. Animals with underlying vestibular disease (think central or peripheral vestibular disease) often have a residual positional strabismus, or mild head tilt, or another lingering deficit. Animals with VE do not! (At least not as far as we know...yet.) In a recent study published in JVIM (2024), the authors identified 10 dogs with suspected VE. All 10 dogs were treated with an anticonvulsant drug (or 2). Five of 10 dogs received just levetiracetam, 2 of 10 received Levetiracetam + phenobarbital, and 1 of 10 received levetiracetam and gabapentin or just phenobarbital. Half of the dogs receiving levetiracetam only had resolution of seizures and the other 5 had a sustained reduction. The one dog receiving phenobarbital and levetiracetam had marked improvement after phenobarbital was added, but not before.

What Is The Take Away Message?

1) Be aware of transient vestibular signs - maybe your patient has seizures!?
2) If seizures are suspected, try levetiracetam (22 mg/kg PO q8h standard release; 30 mg/kg PO q12h extended release)
3) The dogs in this study had idiopathic vestibular epilepsy (because the study selected for those cases) but vascular disease (such as transient ischemic attacks; TIA) can cause transient vestibular disease and maybe vestibular epilepsy (according to a different study).   

Not sure what your patient has? Catch a video and set up a consultation! I'm always happy to rule OUT neurologic disease and I am here to help when we rule it IN. Have a great week! I hope those of you celebrating Easter had a nice, relaxing holiday. I look forward to working with you soon!

Cardiac Changes with Idiopathic Epilepsy?

A recent study from Brazil (www.veterinaryworld.org/Vol.17/February-2024/13.pdf) evaluated 10 dogs diagnosed with Tier I level idiopathic epilepsy to determine if changes to the EKG were present. The rationale for doing this study was initiated by the human epileptic syndrome of "sudden death in epilepsy, or SUDEP". SUDEP is a devastating syndrome wherein human patients are found dead after recovery from a recent seizure. This is most traumatic for the parents of pediatric epileptics who may help their child through a seizure, see that they are recovered and then find them deceased a short while later without any signs of additional seizures. The cause of SUDEP is debated however a cardiovascular cause appears most likely. This syndrome is rarely identified and poorly published in veterinary medicine. 

During a seizure, a tremendous release of catecholamines occurs which may stimulate hypertension, as well as intoxicate the cardiac muscle causing poor relaxation and cardiomyopathy. The study reported findings in 10 dogs with epilepsy and compared them to 11 dogs without epilepsy who were apparently healthy on laboratory testing, physical and neurologic examination and without a seizure history. 

Results

The QRS complex was significantly longer in dogs with epilepsy compared to the control group suggesting left ventricular enlargement or left bundle branch block. Additionally, the QT interval was prolonged, and this was attributed to the below reference range ionized calcium concentrations in the epileptic dogs. Interestingly, the control dogs also had lower ionized calcium concentrations so one might question the validity of this test. What do these cardiac changes mean for us? It means that even "well controlled, healthy" epileptic dogs may have occult cardiac damage. Use caution when providing anesthesia to this group and perhaps reach for a preoperative EKG for this population even if their breed or age wouldn't otherwise spur you to do so. Lastly, I found it interesting that the serum glucose concentration was significantly higher in dogs with idiopathic epilepsy compared to the control group. This likely harkens back to the high sympathetic response and catecholamine release mentioned above but another idea crosses my mind as well. Many internet sites still recommend giving glucose or honey to a pet after a seizure, even without evidence of hypoglycemia. Ice cream, popsicles, and honey are frequent additions to post-ictal care in many of our patients. If given prior to the laboratory samples, it could falsely increase the serum glucose concentration. What's the take away here? Don't rule out hypoglycemia as a seizure etiology on a single blood sample. Consider a second one 4-6 hours later, during hospitalization, and note if the glucose drops below the therapeutic range. (Oh, and make sure your clients are advised against giving sugar products postictal. No one needs a sugar rush when you're on a catecholamine rush!)

Thanks for reading! This little article crossed my radar this week and I thought it was good enough to share with all of you! I hope you have a great first full week of Spring (anyone else looking at snow on their forecast??) and I look forward to working with you soon.

Hypothyroidism and Neuropathies

Does hypothyroidism affect the nervous system? You bet! The peripheral nerve is the most common target in the neurologic system. How does a low thyroid hormone affect the peripheral nerve (you might ask)? I'm glad you asked...

Etiology:

1) accumulation of mucinous deposits resulting in nerve entrapment
2) demyelination secondary to Schwann cell defect
3) vascular nerve damage secondary to hypothyroid induced dysfunction of BBB
4) disruption of axonal transport

Signalment:Typically older dogs, however congenital disease does (rarely) happen. NOTE: dogs are not always overweight, heat-seeking or have flaky-hair coats with peripheral neuropathy signs. 

Clinical signs:A polyneuropathy (multiple nerves affected) is most common. This results in paresis without ataxia and reduced to absent peripheral spinal reflexes. Signs may be mild, to start. 
Cranial nerve deficits such as facial nerve paralysis (VII), vestibular dysfunction (VIII), or laryngeal paralysis (X) are common signs of hypothyroidism. Of course, other things can cause damage to these nerves but don't forget to include hypothyroiism on your differential diagnoses list for patients with a peripheral neuropathy. Hypothyroidism may also cause a myopathy and/or megaesophagus.

Diagnostic tests:T4 is a good first step. If abnormal, a full panel is recommended. 

Treatment options:You guessed it...supplementation!

Prognosis:The neuropathy is likely to improve a little or a lot, after several months with therapy if the axonal degeneration is not too severe. I commonly caution owners to be prepeared for perminent deficits and rejoice when that doesn't happen!
Cranial nerve deficits may persist even with appropriate treatment.

Frequency:
Common in older dogs. Remember they don't need to be over0-weight, heat seaking or even sluggish to get a hypothyroid induced peripheral neuropathy. Cats can be hypothyroid too!

May the luck of the Irish be with you this week! Thanks for reading and have a great week! 

How do I use the Menace Response?

Picture this...You are presented with a 4 year old Pug with a history of "bumping into things" recently. You do a complete physical exam, including a fundic exam and neurologic exam (self high five!) and find the following changes:
Mentation: Quiet, alert and responsive
Cranial nerves: Absent menace OS, intact PLR, intact ocular movements, normal remaining cranial nerves
Gait: normal
Postural reactions: absent left pelvic limb, all others normal
Reflex: normal all limbs and cutaneous trunci
Palpation: non painful.

 
First question: Does this patient have neurologic disease? 

Golly, if it didn't this would be a silly TidBit Tuesday, wouldn't it?  It seems odd to ask this question but I feel it is a good habit get into, to ensure you're not trying to make a non-neurologic problem into a neurologic one. Interestingly, a recent report identified 8% of pets referred to a University Neurology service had "pretenders" disease (ex: cruciate rupture that was mistaken for a neurologic condition). 

Second question: What is the neuroanatomic lesion localization?

Start with basic anatomy. In a very simplistic sense, menace uses CN 2 (sensory) and CN 7 (motor) with a pass through the prosencephalon to connect the two CN. This is a complex pathway that we don't fully understand but the true bare basics are CN2, pass through the prosencephalon and CN 7.  Damage to 2, prosencephalon or 7 will result in a menace deficit. Now, expand the anatomy to include the pathways. The left eye uses left CN 2, crosses and uses right prosencephalon and then back to the left CN 7. 
We still don't know if it is CN 2, prosencephalon or CN 7 that is affected, right? Isolate CN 2 from CN 7 by doing PLR. 
PLR = CN 2, midbrain, CN 3. 
Deduction would say that if PLR is normal then CN 2 must be normal too, right?
Now we need to sort out if the menace deficit is due to disease of the prosencephalon or left CN 7. So, isolate CN 7 from CN 2 by looking at the blink reflex.
Blink reflex = CN 5, and 7.
If you tap the medial and lateral canthus and they blink, CN 5 and 7 must be intact! In the case above, we said all cranial nerve tests, other than the menace response, were normal. Therefore, CN 7 must also be normal. 

 
Voila! Neuroanatomic lesion localization is RIGHT prosencephalon!

What about that postural deficit in the left pelvic limb, you ask? 

That pathway goes from the pelvic toes --> up sciatic nerve -->up left spinal cord --> up left brainstem to cross in the midbrain --> ends in right prosencephalon.

This dog has a right prosencephalic lesion (aka right forebrain) giving both a left menace deficit and left pelvic limb deficit. Well done! You now know WHERE the problem is coming from and can build your differential diagnoses list for a focal prosencephalic lesion and/or refer them to a neurologist (instead of an ophthalmologist) for further testing.

Want more? I can do personalized CE at your hospital. We can go through neuroanatomic lesion localization, discuss seizure cases, or any other topic you and your colleagues might find helpful for your practice. Email me for additional details.

Have a great week and stay warm!

Managing Upper Motor Neuron Urinary Retention in Cats

An upper motor neuron bladder means that the sensory information from the bladder cannot be transmitted to the pons and that upper motor neurons from the pons cannot reach the lower motor neurons of the bladder to cause initiation of bladder expression. To cause this, the lesion is usually cranial to S1. Cats are especially difficult to manually express due to their high external sphincter tone.
Let's look at the bladder innervation for just a moment. The detrusor muscle contracts secondary to innervation that comes from the T12-L1 region via the hypogastric nerve. There are two sphincters, both innervated by nerves arriving from the pelvic plexus (S1-S3 region), that help retain urine. The external sphincter is the only one with voluntary control and that is handled by the pudendal nerve. When we say an upper motor neuro bladder (UMN) we are really talking about anything cranial to the pudendal nerve, that is S1, because that is the only nerve with voluntary control. 

We use manual expression in the acute phase of spinal cord injury to avoid separation of the tight junctions of the bladder wall muscles and, therefore, possible permanent injury to the bladder wall. Manual bladder expression works because pressure is exerted onto the urinary bladder which then forces the internal sphincter open, and eventually the external sphincter as well. Due to the high external sphincter tone occasional urinary rupture has occurred when expressing cat urinary bladders. Dogs appear to have less tone and therefore rupture is less common. A recent study (Galluzzi F, De Rensis F, et al Nov 2023) evaluated 34 cats with UMN induced urine retention secondary to acute or chronic spinal cord injury. They divided the cats randomly into two groups: group M underwent manual expression only and group MT underwent manual expression PLUS tactile stimulation of the perigenital region during expression. Tactile stimulation was described as a rapid striping motion of the perigenital region (from prepuce to scrotum or anus to vulva) over a 30 second period. This technique was copied from how female cats will lick their kittens during the first few weeks of life to stimulate urination.(As an aside - In a small study of cats less than 2 weeks of age, urinary retention occurred if this stimulation was not applied.) With this understanding, Galluzzi et al added tactile stimulation to manual expression to see if it improved bladder expression. In the M group, a urinary stream was achieved in half of cats while the MT group obtained a urine stream in 100% of the cats. Additionally, the stream was obtained in significantly less time (3.75 seconds vs 7.8 seconds). This is so simple, and yet make so much sense!

Key Point
Bladder expression for cats with UMN bladder dysfunction could have manual expression PLUS tactile stimulation applied to improve success rates! 

I hope you enjoyed this week's TidBit Tuesday!  Do you have a case you feel would benefit from a neurology consultation? Please reach out or use the online scheduler to schedule a consultation. This has been an emotional week for many veterinarians that I know; please stay safe and know that my phone and email are always available for you if you need to talk. I hope you have a good week. 

What to do with a narrowed disc space?

Narrowed Disc Spaces

It's a Tuesday morning and on your schedule is a 2 year old MC Labrador retriever with a 2 week history of back pain. The neurologic examination is normal. Without any neurologic deficits, remember that the pet hasn't been diagnosed with neurologic disease (yet), so spinal pain can be due to bone, joint, nerve, spinal cord, muscle or meningeal in origin. You elect to take sedated spinal radiographs and send them off to the radiologist. A radiologist will report what they see, which often includes "narrowed disc space(s)" on the report. What do you do with this?

Does a narrowed disc space indicate a disc herniation?
No, sorry. A narrowed disc space could be positional (often), beam angling (often), due to disc degeneration, or disc herniation. Disc degeneration occurs when hydration leaves the annulus fibrosis, thus causing the disc to shrink a little. This is a normal aging process and does not indicate a herniation. Herniation occurs when part of the disc (annulus fibrosis (AF) or nucleus pulposus (NP)) leaves it's normal position. When the NP leaves, we call it a Type I disc herniation. Type I disc herniations are common in chondrodystrophic dogs and about 30% of non-chondrodystrophic dogs. Clinical signs often include calcification of the NP which might be visible on radiographs. Remember, in situ calcification is appropriate and normal for chondrodystrophic and some non-chondrodystrophic dogs and does not indicate herniation. Calcification in the canal suggests that the disc has herniated but does not indicate that the current clinical signs are due to THAT disc herniation. This means we cannot diagnose a type I disc herniation strictly on radiographs. An MRI, CT or myelogram is needed to diagnose a type I disc herniation. 

When the AF displaces, it is called a Type II disc herniation. This is more common in non-chondrodystrophic dogs and is often part of disc associated wobblers and lumbosacral disease. No calcification occurs for this form of herniation therefore it cannot be seen radiographically. A narrowed disc space often (but not always) accompanies a type II disc herniation but is not always radiographically visible. An MRI, CT or myelogram is needed to diagnose a type I disc herniation. 

What about FCE or ANNPE?
Acute noncompressive nucleus pulposus extrusion (ANNPE) or fibrocartilaginous embolism (FCE) are two more forms of disc herniation where in a small amount of disc material leaves its normal location, often under great force. A narrowed disc space can be seen with these types of disc herniation as well but would  NOT be diagnostic for either disease. An MRI is needed to diagnose an FCE or ANNPE. 

What causes of back pain CAN you diagnose on radiographs then??
The most common causes of spinal pain are 2 "D"s, 2 "T"s and an "M" (as I teach it to students). Discospondylitis, disc herniation, trauma, tumor, and meningitis. Of these, only discospondylitis, vertebral neoplasia and fracture/subluxation can be diagnosed on plain radiographs.

The patient above could have discospondylitis on their differential diagnoses list therefore radiographs are absolutely indicated. However, please be cautious reading too much into a "narrowed disc space" and instead look for discospondylitis, vertebral neoplasia or signs of trauma. 

I hope you enjoyed this week's TidBit Tuesday! We're almost into March which, if you're a long-time patron, you know means we're approaching St. Patrick's day. My girls are Irish Dancers and, as such, usually perform in over 30 shows in the month of March. That means this proud mamma has a more limited work schedule due to all of the driving so PLEASE reach out if you cannot find a suitable time on the online scheduler. I may (often can) shift things a bit to accommodate your request! Have a great week and stay safe out there. 

Which Reflexes Should I Do?

Have you ever looked down at the patient, laying calmly and quietly in lateral recumbence, and thought “okay, which reflexes do I do?” There are several choices for each limb, but the most commonly assessed reflexes are as follows:

• Thoracic limb (I was trained by Dr. DeLahunta and was taught to never call this the front limb, but you are welcome to do so!): Biceps, triceps, extensor carpi radialis and withdrawal.

• Pelvic limb (same story as above): patellar reflex, cranial tibialis, gastrocnemius and withdrawal.

Some of these reflexes are harder than others to observe and obtain. The purpose of performing the spinal reflexes is to assess the sensory and motor pathways associated with that specific peripheral nerve and the spinal cord segment. For example, the patella reflex evaluates the femoral nerve and the L4-6 spinal cord segment. A present reflex suggests this pathway is intact. An absent reflex suggests that the peripheral nerve (femoral nerve) and/or the L4-6 spinal cord segments are NOT intact. A recent study (Chiang B, Garia G, et al 2024) evaluated each of these reflexes in 101 dogs and asked 1 neurologist and 1 resident to determine if they were obtained, or not (simple binary question).
Several of the reflexes had high intraobserver agreement, which would suggest that these are both easy to detect and possibly easier to obtain. The reflexes which high intraobserver agreement included the extensor carpi radialis, withdrawal reflexes in both thoracic and pelvic limbs, patellar reflex and cranial tibial reflex. Although all reflexes could (might I say should?) be attempted in the neurologic examination, sometimes we don't have this luxury. From this study, I would suggest that the 4 reflexes mentioned above should be reliably present. If you perform these reflex tests and do not observe a response, it is reasonable to consider them absent or delayed. 

Not sure how to perform these reflexes? I run personalized CE events, including live animal neurologic examination practice, in your clinic. Email me to learn more or to schedule. 
Does neurology make you nervous?? Please reach out to schedule your patient for a neurologic examination or reach me via email with any questions. My job is to help you decide if a patient has neurologic disease, or not, and the way we do this is to utilize the neurologic exam.

Thanks for reading. This article can be found here:DOI: 10.1111/jvim.16999

How Effective is Zonisamide in Cats?

Seizures are a common reason for me to evaluate cats and therefore (I assume) something you encounter frequently. Seizures originate from the forebrain (prosencephalon) and can be secondary to idiopathic epilepsy, structural epilepsy (such as congenital disease, neoplasia, meningoencephalitis, cerebrovascular events, head trauma, and on goes the list), or metabolic seizures (hypoglycemia, thiamine deficiency, etc.).

The mainstay treatment for cats has been phenobarbital for many years and not without good reason. Phenobarbital controls seizures in over 90% of cats, regardless of the etiology, and has predictable clinical side effects. When cats cannot tolerate phenobarbital, or have seizures in excess while on phenobarbital, other antiepileptic drugs (AED) are added; one of those is zonisamide. Very little data has been published to date about zonisamide use in cats. A recent study out of UW (go Bucky) was published recently. I thought it was worth a quick summary, TT style.

How many cats were enrolled in this retrospective, multicenter study? 57

The median age of seizure onset was 7 years (range 0.17-22) and the median age of onset for cats diagnosed with idiopathic epilepsy was 8 years. Note the difference between cats and dogs! Dogs have a lower median age at onset! Importantly, note that 30 cats did not have advanced diagnostics (52%) which means a final diagnosis was not reached and therefore their disease may have affected their response to zonisamide (but we don’t know!).
How did the cats on zonisamide respond to treatment?

• There was a significant decrease in seizures/month AND seizures/day after starting zonisamide. Note: we don’t know how long the seizures were monitored before starting zonisamide.

• 70% of cats responded to zonisamide monotherapy (had less than 1 seizure per 3 months)

• 56% of cats responded to zonisamide as add-on therapy

• Almost 70% of cats diagnosed with idiopathic epilepsy responded to zonisamide but it isn’t clear if these cats were on monotherapy or add-on therapy.

• The median dose was 7.5 mg/kg/day with about 1/3 of the cats receiving the drug once daily and 2/3 receiving it twice daily.

• More cats obtained seizure control on twice daily dosing than once daily dosing but the side effects were more profound on twice daily dosing.

• Side effects were noted in 15/57  cats and they included inappetence (10 cats), sedation, ataxia and vomiting for most reports. The duration of the side effects was up to 4 weeks after starting the medication. This is surprising and warrants further investigation. Anorexia has been the side effect I note more commonly but

• No clinically significant CBC or biochemistry changes were noted on the cats in this study

So what’s the take home message? Would I use zonisamide in a cat? A qualified, yes. Phenobarbital still has a better reported seizure control compared to this cohort of cats on zonisamide. BUT it is worth a try if the cat fails treatment with phenobarbital and the don’t have a history of a sulfa drug reaction (zonisamide is a sulfa derivative). Starting dose should be less than 10 mg/kg daily, and side effects appear dose dependent…but last awhile!

Thanks for reading this week’s, TidBit Tuesday! I hope you learned a little something – I know I did! Keep those consults rolling. Have a great week and stay warm and safe out there.
 
 Reference: https://doi.org/10.1111/jvim.16984

Anesthesia for Pets with Seizures

It’s a Tuesday morning, and on your schedule is a 6 year old Maltese dog with a 3 year history of seizures that appear well controlled on phenobarbital monotherapy. She has a history of 1 seizure every 6-8 months and each seizure is less than 3 minutes in length. No interictal signs noted by the owners and she continues to have a normal neurologic exam. Today, they would like to discuss doing a dental for their dear little dog. What should you consider? How does general anesthesia for a patient with neurologic disease differ from those without?

The Risks of Anesthesia

General anesthesia is not necessarily bad. 😊 The biggest two risks of general anesthesia for dogs or cats with seizures are (1) hypotension and (2) negative effect on the seizure threshold. Let’s talk hypotension.
Your goals are to preserve cerebral blood flow, which is largely controlled by the cereal perfusion pressure, which is largely controlled by the mean arterial blood pressure (MABP). MABP is directly related to intracranial pressure (ICP). Thankfully there is a wide range at which MABP will have little negative effect on ICP. MABP between 50-150 mm HG should result in constant ICP, if other parameters are equal. Hypotension can be caused by some of the medications used (I’m looking at you acepromazine) or caused by CO2 levels. If the PaCO2 levels are above 50, a risk of vasodilation occurs which may decrease MABP. Monitoring CO2 can be quite useful to avoid this. If vasodilation occurs, and consequently decreased MABP, perfusion to the brain can be compromised. Hyperventilation will decrease the PaCO2, result in vasoconstriction and maybe lower the ICP. Some references suggest that PaCO2 should be between 30-35 for “appropriate” cerebral perfusion. Big disclaimer today – I am not an anesthesiologist so specific questions about anesthetic protocols should be directed to your local anesthesiologist! Long-standing, serious, hypotension can affect neuronal membranes and in rare situations could cause neuronal cell membrane damage, or a worsening seizure disorder. Thus, try to keep the PaCO2 in a normal range, and monitor blood pressure for pets with seizures undergoing anesthesia. 
With respect to the seizure threshold, isoflurane, diazepam, midazolam, and possibly propofol are neuronal protective. If you have the luxury of choice, consider using one (or all!) of these medications in your anesthetic protocol. If you have a patient with poorly controlled seizures, administration of IV phenobarbital 20 minutes before starting anesthetic recovery may be useful to add seizure protection during the recovery process. ALWAYS go slow! Give the phenobarbital over 20-30 minutes as a slow infusion to avoid severe cardiovascular or respiratory suppression. This drug is closely related to pentobarbital, our common euthanasia solution. Most patients can receive benzodiazepine medication if active seizures are noted during the recovery process. Paradoxycal hyperactivity following benzodiazepine adminsitration occurs rarely but would be a reason to avoid using the drug in the future if a patient exibited these signs. Patients with significant hepatic disfunction such as those with portosystemic shunts should either avoid benzodiazepine drugs due to inadequate metabolism, or be adiminsered a 25% dose. 

Any anesthetic event, even an uneventful one, can put a patient with a known seizure disorder at risk for seizure breakthrough. This risk persists for at least 24 hours following anesthesia but in rare patients it can be longer. Owners should avoid leaving the pet alone for extended periods of time such as traveling by airplane, boarding the pet or other unobserved time in the first 24 hours after anesthesia. Never withhold chronic anticonvulsant medications prior to anesthesia. Bromide can cause vomiting therefore it should be given with a small meal. Patients receiving bromide (liquid) can receive it rectally if they are anesthetized early in the morning and a small snack with their bromide is not possible. Phenobarbital, levetiracetam and zonisamide can be given on an empty stomach without high risk of GI upset.

This topic was suggested by one of your colleagues - thanks for the suggestion! Do you have a topic you wish I’d cover? Please reach out!  Thanks for reading and have a great day!

Limping - Orthopedic or Neurologic?

Limping is often orthopedic in origin however in some situations limping can be of neurologic origin. Nerve root signature (NRS) sign is observed clinically as a non-weightbearing flexion of one limb, during standing, which may also appear like limping when gaiting. The suspected causes for NRS include vascular compression, inflammation or compression of a nerve root. This is most commonly noted in the thoracic limbs but has been reported in the pelvic limbs also.
In a recent study, a group from NCSU evaluated dogs with cervical disc herniations to see what criteria were present when they had signs of a NRS. This study included 47 dogs. Not surprisingly, all 47 had signs of cervical hyperesthesia with signs like ataxia (n=14), intermittent lameness (n=7), tetraparesis (n=2) and tetraplegia (n=1) being observed less frequently. I personally am not sure how you can identify a dog with a root signature sign if they’re plegic…but apparently, they did! Interestingly (to me) the site of disc herniation was C2-C5 in 20 dogs (43%) and C5-T1 in the other 27 dogs (57%). The nerve roots are supposed to arise from the C6-T2 region which is why it would make the most sense that a NRS sign should involve those nerve roots. Why did the C2-C5 region have NRS signs? Perhaps there was tethering of the nerve roots from "tugging" secondary to a cranially located disc. Perhaps anatomically they had a neve root arise more cranial than typical.
Spinal cord compression was mild in the majority of cases but remember it takes a TON of disc material in the cervical spinal cord to result in compression. Mild spinal cord compression is often surgical because the canal is much more voluminous around the smaller spinal cord (which is different from the thoracolumbar spine). Therefore the canal can contain loads of disc material yet the spinal cord has room to scootch over away from the disc, thus resulting in mild compression. Disc material was almost 3x more likely to be located laterally, within the spinal canal, than medially. Additionally, dogs were 2x more likely to have disc material compressing a nerve root compared to dogs without NRS. The last interesting finding is that 75% of the dogs in this study were over 7 years old. Typical chondrodystrophic disc degeneration with resulting herniation occurs in ages 3-7 year old. Is there a relationship between age, site of disc herniation and NRS or was this coincidental? I’m not sure but felt it was worth of comment.
 
Take away message:
Thoracic limb limping is often orthopedic in origin, however NRS should be considered for cases in which orthopedic disease is not identified. Nerve root signature sign secondary to a cervical disc herniation is more likely to be lateralized and therefore referral for surgical correction is strongly recommended to alleviate the compression to the nerve root.
 
Thanks for reading! Are we through deep winter? I’m not sure but I sure hope you’re staying warm! Please reach out with any questions about root signature sign or other neurologic cases. Have a great week!

Heat Tilt, Turn or Neck Turn...so what?

Does a head tilt help with neurolocalization?
 

A recent study by Nagendran et al (The value of a head turn in neurolocalization, JVIM 2023) described 4 distinct areas of neuroanatomic lesion localization for head turn, head tilt and neck turn and looked at head and body position in each of these localizations. If you see a patient with their head deviated to one side yet parallel to the floor, that would be a head turn. If a patient has their head deviated to one side NOT parallel to the floor, we would consider this a head tilt. The head tilt can be anything from 1-90% from the x axis! If the neck is turned to one direction it would be called torticollis and may be (and often is) associated with either head tilt, head turn, or both. This recent article looked at these three signs, in reference to the neuroanatomic lesion localization, with the goal of trying to sort out the underlying neuropathology (totally cool but not "light reading" and therefore saved for another conversation).
Key Points:

• Forebrain disease – The majority or patients had an ipsilateral head turn, with less than ½ of the dogs demonstrating ipsilateral body/neck turn.

• Brainstem disease – All dogs had an ipsilateral head turn, and 5/9 had an ipsilateral head tilt, with a rare dog demonstrating a neck turn.

• Cerebellar disease – All dogs had an ipsilateral head turn and the majority had a contralateral head tilt with a rare neck/body turn noted showing a contralateral neck/body turn.
  

• Cervical spinal cord disease – all dogs had a contralateral head turn along with a majority (6/7) showing a ontralateral head tilt.

Summary:

• Head turn ONLY – consider forebrain disease

• Head turn with neck turn (ipsilateral) – consider forebrain disease, but the neck turn is an inconsistent finding in many dogs with foreain disease.

• Head turn, neck turn AND head tilt – most likely cervical spinal cord disease but cannot rule out cerebellar disease.

• Head tilt only – likely brainstem disease (or peripheral vestibular disease!)

Take Home Points:
A head tilt, head turn, or neck turn is a useful physical examination finding to point you at neurologic disease however they aren’t discretely localizing on their own. Using the information above, you may be able to support a localization noted in concurrence with your other neurologic findings.

Thanks for reading! I made the difficult decision to increase my consultation fees this year so if you didn’t get an announcement please reach out and I can send you the updated fee schedule. Lastly, it’s winter!! That means sometimes travel can be hazardous and cancelations can happen. I don’t charge if we cancel due to inclement weather and will do my best to work your patient into the schedule as quickly as possible afterwards. I appreciate your business very much and do my best to meet your expectations. Have a great week!