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. 

Long-term infection and monitoring of Brucella suis in dogs

B.suis, you say? Why do I need t know about a swine variant of Brucella?? Did you know that B. suis can be pathologic in dogs, as well as swine, and is also zoonotic? You're welcome :)

A recently published article detailed the clinical signs, blood work, imaging (when available), serologic progression over time, and body fluid levels of organism over an 18 month period in 27 dogs from 17 households. The study population was located in Australia where naturally occurring B. canis is not found. Exposure to feral pigs was considered an important source of disease acquisition and may be a stand alone reason to test. (1 in 10 pigs are positive in Australia.) Although B. suis is not as commonly noted in our US canine population, we are a global veterinary profession now with lots of dogs traveling or being adopted from international locations. I felt this article was a nice reminder that B. suis exists, and is pathologic in dogs as well as having zoonotic potential, like B. canis. 

Clinical Signs of B. suis

Ten dogs had clinical signs attributed to brucellosis. Clinical signs included pyrexia with orchitis and epididymitits (4/10), lymphadenopathy (1/10), spinal pain (3/10), abortion or dystocia ( 1/10), and athritis (2/10). The remaining 17 dogs were assymptomatic throughout the entire 18 month period!

Serology and PCR

Titers did not correlate with severity of signs. Postive results were deemed positive if a Rose Bengal rapid plate test (RBRPT) yielded a positive result along with a complement fixation test (CFT) greater than or equal to 8. Only 2 dogs had seronegative results after 18 months and both had low baseline serology. Brucella DNA was not detected by PCR in blood, urine, saliva or preputial swabs in any dog at any time in the study. Notably, they weren't swabbed weekly or daily, so it is possible that some shedding occurred without detection on the sporadic testing. Only 3 positive PCR tests were found and this occurred in 1 bitch post whelping (vaginal fluid), as well as milk at 3 and 7 weeks post whelping as well as a lymph node at necropsy on a puppy that died. Although culture may be the gold standard diagnostic test for some countries, the RBRPT and CFT were considered safter to personnel performing the test and were preferred in this study. 

Diagnostic Imaging Results

Fifteen dogs had some sort of radiograph taken during the study period. Two of 15 had joint siease, 3/15 had vertebral lesions and 2 of 15 had lymphadenopathy. The dogs with radiographic changes had spondylosis, which we know can be a normal finding, therefore I question the inclusion of this as a clinical sign of brucellosis. 

Treatment Response

Six dogs were treated with doxycycline and rifampicin (one dog relapsed and was treated twice. It was generally well tolerated with one case of marked hepatitis. There is no standardized treatment for brucella and many dogs are considered to harbor the bacteria long-term, with or without clinical signs, with intermittent bacteremia. The zoonotic risk to humans, therefore remains present with dogs with a current or historic positive Brucella test. Euthanasia is the recommended treatment for positive livestock, however this causes emotional conflict for veterinarians and owners of companion animals. Check with your local veterinary health directors to determine the legal requirements in your state or country. This is a reportable disease in the USA. 

If you'd like to read more about this study you can find it here: https://onlinelibrary.wiley.com/doi/epdf/10.1111/jvim.16678

In honor of Memorial Day yesterday, I wish to thank all of you that have served or have friends or family members that have been lost during military service. We honor you!

Have a wonderful week! My schedule has changed for summer so please reach out if you cannot find a suitable time for a consult online - I may have additional flexibility that isn't listed. 

Renal Tubular Acidosis and Zonisamide

Ahh, it is time to examine Zonisamide again. A recent article in Veterinary Medicine and Science described a single dog with lethargy and distal renal tubular acidosis following administration of zonisamide. (https://onlinelibrary.wiley.com/doi/epdf/10.1002/vms3.905)
Distal renal tubular acidosis (RTA) has been defined as a normal anion gap metabolic acidosis with alkaline urine.

What should I look for to diagnose RTA?

The dog in this report had hypochloremia and hyperkalemia on initial blood work. This, coupled with a mild acidosis on blood gas and a urine pH of 7.73, suggested RTA. We're not sure of the consequences of RTA in dogs, yet. In pediatric human epileptic patients, there is some concern for future renal disease with RTA but this hasn't been well established (to my knowledge) for dogs. In this case, the link between the RTA and the dog's clinical lethargy was made, which is what drove the clinicians to pursue treatment.

How is it treated?

The authors described a very slow infusion of bicarbonate (please don't do this unless you have 24 hour monitoring capability!) which reversed the clinical lethargy and normalized the blood gas imbalance for 3 days. They did try to reduce the dose of zonisamide prior to treating the acidosis and achieved mild clinical improvement of sedation when the serum zonisamide concentration went from 38.6 ug/ml to 15.1 ug/ml. No change in biochemical status was noted. If you don't have the option to do a bicarbonate infusion, slowly tapering down or off of zonisamide is recommended to reverse the RTA. It is unknown, in dogs, if sustained RTA has negative health consequences. For many patients, another anticonvulsant drug must be substituted prior to removing zonisamide from the treatment plan.

Another short, but sweet TidBit Tuesday. Please let me know if you have any questions!
I hope those of you here in Wisconsin enjoyed the wonderful weather we had this past weekend and have found your winter hats and gloves in preparation for this coming weekend. Bring it on, am I right??

Recurrent Cervical Pain

Imagine with me that you are presented with a 10 kg small breed dog on Tuesday morning with a history of neck pain. This dog had a history of neck pain 1 year ago that underwent full work up, at your local University or specialty hospital, and was diagnosed with a disc herniation. The clients pursued surgery, and recovery was smooth and complete. The clients were thrilled...until yesterday. Now, they're angry.

How likely is it that this dog has herniated ANOTHER disc in it's neck?

It is a good question, and one that we have some recent data that might help answer this question. A study out of the UK looked at the recurrence rate of cervical pain in dogs that had a prior disc herniation diagnosed via advanced imaging.
119 dogs in the study, 36 dogs had signs of recurrent neck pain or a cervical myelopathy.

• 36/119 had medical management following diagnosis of IVDH

  • 13/36 (36%) had a recurrence of signs

  • Recurrence was more likely at the same intervertebral disc space

• 83/119 had surgical correction following diagnosis of IVDH
  

  • 27/83 (33%) had a recurrence of signs

  • Recurrence was more likely at neighboring intervertebral disc space to the original disc herniation

• Surgical correction did not decrease the odds of recurrence in this study. Important: We don't know if these dogs underwent surgical fenestration at the time of their first surgery, or not.

• Recurrence was within 2 years of the original diagnosis of a disc herniation for 80% of the dogs in this study. (Note: this means that 20% it was longer than 2 years!)

** We don't know that every one of the dogs had a second disc herniation but the few that did have work up did have a disc herniation confirmed.

The data reported in this study suggests that medical and surgical correction of cervical disc herniations does not change the risk of new onset cervical pain. Reported ranges in the literature for recurrence of cervical pain with surgical correction are between <10-30% (and probably more towards the 0-15% range in the cervical spine) so it is at the high end of reported recurrence. Reported recurrence with medical management is slightly more difficult to track but may be in the 30-40% range. Therefore, it is surprising that the authors saw a similar recurrence for medical vs surgical correction. This may come down to the surgical correction performed, which we don't know from this study. We do know that none of the dogs with surgical correction had a recurrence at the site of correction.

What should we tell the client before us? Surgical correction for a ruptured disc corrects the issue at that disc, but may not address degeneration at distant sites. Sadly, their pet may be faced with a recurrence of another disc herniation. If they're up for another workup and possible surgery, it's time to start the process for referral. If they'd like to give medical management a try, get started on some pain management and bed rest (avoid those steroids if you can in these cases!) and keep a close eye on the dog. Weekly neurologic exam would be recommended, if possible.

Link: https://onlinelibrary.wiley.com/doi/epdf/10.1111/jsap.13480

This Tidbit took a slightly different approach than my usual updates. I typically try to pull 1-2 key points from an article that I find useful, and that I think you'll find useful. This time, I decided to represent a study that wasn't highly powered, that also didn't provide clear, convincing data to support a specific question. We all like black and white scientific data that we can read, digest and apply but honestly, that is a minority of what I read on a daily basis. This TidBit had more "waffling" in it because I wasn't fully convinced the data provided would change my practice. How did this report strike you? Did you find it useful, or not? As always, thanks for reading!

Have a great week and keep those consults rolling!

NSAIDs vs. Prednisone...What Do I Do??

Case 1: A 4 year old Dachshund with 3 day history of back pain. On neurologic examination you find spinal pain at TL junction with reduced paw replacement in both pelvic limbs, normal reflexes and normal gait analysis. Neuroanatomic lesion localization (NALL): T3-L3 myelopathy
What would you rank for a differential diagnoses list?
I'd consider IVDH, meningomyelitis, discospondylitis and neoplasia.

Case 2: A 1.5 year old FS Cavalier King Charles spaniel. On neurologic examination you find moderate cervical spinal pain with reduced paw replacement in the left pelvic limb and marked phantom scratching at the neck when lightly stimulated.
NALL: C1-C5 myelopathy
What differential diagnoses would you consider for this case? I would suspect syringohydromyelia first, followed by less likely meningomyelitis and IVDH.

Case 3: A 2 year old MC Labrador with lumbar pain, a normal neurologic examination and fever of 102.0F.
NALL: Lumbar pain (You cannot have a NALL without neurologic deficits!)
What is your differential diagnoses list for this patient? I'd consider discospondylitis, type II disc herniation, and some non-neurologic causes such as musculoskeletal injury or joint infection. Rarely we see referred pain from prostatic disease (cysts, neoplasia, prostatitis).

We know we need anti-inflammatory medication for pain management, right? Which one?

Case 1: The risk is low for infectious disease in this patient. For confirmed IVDH, neither prednisone or an NSAID has been shown to be superiors for pain control. Without a confirmed diagnosis, we must treat for the top 1-2 differential diagnoses, right? I typically start with NSAID therapy for these patients and if they are unable to proceed with MRI/spinal tap to obtain a definitive diagnosis and clinical signs of pain persist, I switch to prednisone after an appropriate washout period. Is it wrong to start steroids? No. The side effects of GI upset, ulceration and mild immune suppression make them less desirable when treating IVDH but they are not contraindicated.

Case 2: This case has a high likelihood of Syringohydromyelia (SHM) based on the breed and clinical signs. SHM has a high amount of neuropathic pain, which can be mediated by COX-2. Therefore, NSAIDs that target COX-2 may provide some relief. That said, steroids mediate sympathetic pain, decrease substance P expression and decrease expression of lots of inflammatory mediators and may decrease CSF production to boot. Therefore, with a low infection likelihood in this pet and high likelihood of SHM, prednisone is my drug of choice over NSAIDs. If you haven't confirmed the diagnosis, however, it is worth a discussion about the possibility of worsening clinical signs and the side effects of steroids prior to starting the drug.

Case 3: This dog has a high risk of infectious disease based on breed, age and clinical signs. Therefore, in addition to taking radiographs to try to find this dog's discospondylitis (!!), I would NOT use prednisone in this patient. NSAIDs provide wonderful bone penetration and excellent periosteal block of COX-2 mediated pain and would be my drug class of choice.

Steroids, especially prednisone, are not evil and they have a time and a place in neurology. (Understatement of the year😂 ) However, they have a greater chance of adverse clinical adverse effects than NSAIDs therefore they are not needed for every patient with spinal pain. Develop a differential diagnoses list that fits your patient before deciding between NSAIDs and prednisone. Still not sure? Call/email me to discuss your case, or set up a neuro consult!

Heads up - I will be on vacation May 29-June 5th and will have limited telephone and email access. I will respond to emails as I am able but will not be as prompt as usual. Please plan to schedule consults around this window as well. Thanks for your understanding, and support of my small business. I look forward to working with you soon!

Back Pain + Fever

The 2 year old MC Poodle with Back Pain

It is Friday afternoon, and you are about to evaluate a 2 year old Poodle with a recent onset history of reluctance to walk. Upon examination, you find back pain at TL junction and a fever or 104 F. The dog stands there, hunched, but has a normal neurologic exam (self high-five!) and normal remaining physical exam so.... now what?

When I hear this story, my first thought is of discospondylitis. (My second thought is steroid responsive meningitis-arteritis (SRMA), one of the many forms of inflammatory non-infectious meningitis. Let's talk about this another day.)

EtiologyBacterial or fungal infection of the vertebral end plates. Commonly Staphylococci, with other causes including Streptococcus, E. coli, and less commonly B. canis. B. canis is zoonotic and can cause abortion in humans so exercise caution when managing a dog with discospondylitis.

Hematogenous is the most common source, with less common direct transmission (bite wound, grass awn).

Fungal infection with aspergillus or coccidiomycosis (SW USA) most common fungal isolates. Rarely blastomycosis.

SignalmentYoung to middle aged dogs, rarely cats.
Large breed male dogs are more often affected (male: female ratio 2:1).

Clinical signsAcute pain, often with fever, anorexia and other signs of systemic illness. Signs of a myelopathy may develop if empyema occurs, or vertebral subluxation/fracture due to loss of bone integrity. <-- EEK!

Diagnostic testsSpinal radiographs may lag 3 weeks behind onset of clinical signs; however, they are an easy diagnostic test with high yield for many cases. If unrewarding and the index of suspicion is high, spinal CT and then MRI provides increasing better detection rates in early disease.
Or, you can treat the pet for suspected discospondylitis for 2-3 weeks and re-radiograph to confirm the diagnosis.

Treatment optionsAntibacterial or antifungal treatment based on blood, urine or disc cultures. If cultures are negative (approximately 30% of cases have no growth), broad spectrum bone penetrating antibiotics are recommended until radiographic resolution is obtained (maybe 9+ months). These include cephalexin, enrofloxacin and sulfa antibiotics. Pain management and exercise restriction in the early stage of disease is important.

PrognosisFavorable with appropriate treatment.

You're doing great!! I really enjoy helping you, help your patients, live their best lives with neurologic disease. Not sure what to do with a case? You can email or telephone with case questions or schedule a consult online at a time that works for you. (Vets and vet staff only, please!)

Large Breed Dogs and Disc Herniation

A little background...

Dogs greater than 10 kg experience type 2 disc herniation more frequently than type 1 disc herniation. (Refresher: Type 1 = acute extrusion of the center of the disc; Type 2 = bulge of outer ring of the disc into the spinal canal.) An estimated 10-30% of the time large breed dogs have type 1, depending on the study.

How is a type 1 disc herniation different for a large breed dog?

The answer is rather obvious, but glossed over frequently. They are bigger! That means nursing care is harder, surgery takes longer and is more extensive, and as a result there can be a greater expense for some of our larger dogs.

Does the prognosis change for a medium to large breed dog?

Yes. Dr. Woelfel from NCSU recently published data from a cohort of dogs > 10 kg that had both acute disc herniation and extensive spinal cord hemorrhage.

(Spinal cord hemorrhage occurs infrequently for large and small breed dogs and was shown in a few studies to have a minimal effect on prognosis as a stand alone feature. Meaning, the prognosis was still mostly based on the presence or absence of deep pain and didn't depend on spinal cord hemorrhage identified on advanced imaging.)

Okay, back to big dogs with disc herniation and spinal cord hemorrhage. The NCSU study reported a worse prognosis, and a higher complication rate, compared to overall data for small breed and chondrodystrophic dogs.

The details in summary:

• No deep pain before surgery, recovery about 38% (general population: 50%)

• Deep pain present before surgery, recovery rate about 77% (general population:90-95%)

• Complication rate was about 24% (general population: 10-15%)

Post Operative Complications Noted in the Referenced Study

• Decubital ulcers

• Pneumonia

• Self-mutilation

• Fever of unknown origin

• MDR UTI

• Sudden death

• Progressive myelomalacia

What is the take home message?

When talking with an owner of a medium to large breed dog with acute onset paraplegia, I suggest emphasizing the need for intense at-home nursing care, possible complications (along with the higher incidence) and a realistic prognosis if the dog is diagnosed with a disc herniation on advanced imaging. Remember that other differential diagnoses can cause acute onset paraplegia! Please do not interpret this paragraph as a call for euthanasia for large breed dogs with acute paraplegia. A 38% recovery rate is not zero! But a honest, open, vet-to-client discussion is the best way to achieve an informed decision for the client.

Not sure if you are interpreting the neurologic examination appropriately? Not sure if you are doing the neurologic examination properly? Please reach out! I am happy to work with you to help guide your clients in a compassionate and informed way.

Happy Easter to those that celebrated last weekend. We welcomed spring with big smiles around my house this weekend!

Reference: Woelfel, CW, Robertson, JB, Mariani, CL, Muñana, KR, Early, PJ, Olby, NJ. Outcomes and prognostic indicators in 59 paraplegic medium to large breed dogs with extensive epidural hemorrhage secondary to thoracolumbar disc extrusion. Veterinary Surgery. 2021; 50: 527– 536. https://doi.org/10.1111/vsu.13592

Steroid Responsive Meningitis-Arteritis

It's a cold Tuesday morning and your first patient today is a painful, 6 month old Boxer dog. You dutifully run through the differential diagnoses in your head as you walk into the room. What you see when you arrive is a depressed, febrile Boxer puppy trying really hard not to move their head or neck and wincing when doing so.
After examination you find the dog has the following neurologic examination findings:
Mentation: QAR, especially for this normally hyperactive puppy
Cranial nerves: normal
Gait: stiff, stilted gait but no evidence of paresis, ataxia or lameness. (Although lameness and paresis CAN happen with steroid responsive meningitis-arteritis, a.k.a. SRMA)
Postural reactions: normal paw replacement in all four limbs
Reflexes: normal in all four limbs, normal c. trunci and perineal (you did a great job!)
Palpation: Oh how the dog winces with cervical palpation! (Don't do cervical ROM on this dog, okay?)

Neuroanatomic lesion localization: Well...technically the neurologic examination is all normal, right? So all you can say is "cervical pain" on the record. No neuroanatomic lesion localization when they are neurologically normal.

Differential diagnoses: Trauma, fracture, subluxation, muscle strain, infection/polyarthritis, and yes, SRMA.

What is SRMA?

It is an immune mediated disease that affects the vasculature of the meningitis, and sometimes the joints and it typically affects dogs < 2 years of age, with large breed dogs and beagle dogs over represented.

How do you diagnose it?

First, rule out other causes (radiographs, spinal MRI). Next, perform a spinal tap and identify a neutrophilic pleocytosis (often with a SUBSTANCIALLY increased cell count!). Third, rule out infectious diseases that cause meningitis in your area of practice. For most of us in Wisconsin, this is Neospora (toxoplasma if cat), fungi, and bacterial causes.

What is the recommended treatment?

Steroids at 1-2 mg/kg PO q12h, depending on the literature. I start with 1 mg/kg PO q12h for 30 days and then reassess the CSF. Some studies suggest doing this dose, or a slightly tapered dose, for up to 3 months and then reassessing the CSF. When normal, a gradual taper over 3-6 months is common. Relapses can occur in up to 80% of the studies published but my experience has been a much lower recurrence rate.
A recent study by Giraud et al* found a lower relapse rate with the addition of azathioprine. They used 2 mg/kg PO q24h x 1 month and then tapered from there to an every other day dosing interval for 2 months for a total of 3 months of treatment. The authors suggested that the addition of azathioprine allowed them to reduce the prednisone dosage sooner and more rapidly, thus reducing long-term side effects. Over 80% of the dogs in this study were in clinical remission within the 2 year follow-up time without signs of relapse.
Azathioprine was also reported to have exceptionally long survival times when used in combination with steroids to treat meningitis of unknown etiology (MUE), another immune mediated CNS disease. So...perhaps we're on to something here! Interestingly, azathioprine was suspected not to cross the blood brain barrier initially. Hummm...

Key Points:

• SRMA is often treatable, but relapses do occur.

• A CSF tap is needed to confirm the diagnosis however MRI is often performed before CSF to rule out physical/structural abnormalities. This helps to decrease the risk of harm from a spinal tap.

• Steroids are the mainstay of treatment but azathioprine may be added to allow a more rapid reduction of steroids (thus reducing long-term side effects from steroids).

Have a great week and stay safe out there! It's been a snowy few weeks here in Wisconsin so drive safely if you're out and about!