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.

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

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!

How to Localize a Cranial Nerve

As we sit here at the head of the year, I cannot think of a better time to review the cranial nerves. (Yes, I like cheesy jokes. I have kids. Here's another: what's the best present? See the bottom for the answer.)

First important thing to remember about cranial nerves: all cranial nerves except I and II have cell bodies associated with a specific brainstem segment. You might even argue that CN II localizes to the thalamus, which is an embryological part of the brainstem but...well, then we should have a coffee and get to know each other better!  Let's stick to the idea that CN III-XII have cell bodies in specific brainstem segments, thus making it possible (dare I say easy??)  for us to localize a lesion to either a specific brainstem segment OR the peripheral nerve. 

What are the names of the brainstem segments, again? (Mesencephalon, metencephalon, myelencephalon). Okay, whew! Now that that is over, how do you decide if a deficit is coming from the nerve nucleus in the brainstem OR the peripheral nerve?

Take the following steps:

1. Identify the cranial nerve affected (i.e. facial nerve = CN 7).

2. Identify the segment of brainstem associated with the nucleus of this cranial nerve. Don't remember what cranial nerves are associated with which brainstem segment? Midbrain = CN 3,4; Pons = CN 5, Medulla = CN 6-12

3. Are any ipsilateral long tract deficits (postural reaction deficits, hemiparesis) or mentation changes (obtunded, stupor, coma) present?

   1. If yes, the lesion is in the brainstem segment associated with the cranial nerve (i.e. medulla).

   2. If no, the lesion is affecting the peripheral portion of the affected nerve

Guess what? You can apply these steps to any deficit affecting CN III-XII. Yay!
 
Do you need help performing the neurologic exam? I'd love to help! Looking for the answer to the joke? The answer is: a broken drum! You just cannot beat it. Thanks for reading and Happy New Year!

Case Based Practice

Lesion localization is one of those things that can be lost, if not practiced. This week, we’re going to work out those muscles.

Maria, is a 13 year old FS Lab
History: Presented to me with a 24 hour history of acute onset difficulty walking. 

Neurologic examination:
Mentation: BAR
Cranial nerves: right head tilt, rotary nystagmus, remainder normal.
Gait: Moderate vestibular ataxia, falling right. No hypermetria or intention tremors noted. 
Postural reactions: absent right thoracic and right pelvic limbs, normal other limbs
Spinal reflexes: Normal all limbs, normal c. trunci and perineal
Palpation: non painful, normal cervical ROM

You know what you've got to do now, right?

What is the Neuroanatomic Lesion Localization?

There are several ways to go through lesion localization.

OPTION 1:
I like to make lists. Start by listing all of the abnormalities and ALL possible locations that could result in an abnormal finding. For example:
1) Right head tilt - peripheral CN 8 (right), medulla (right), cerebellum (right or left)
2) Rotary nystagmus - same as above
3) Vestibular ataxia - same as above
4) Reduced paw replacement right side - right C6-T2, right C-C5, right medulla, right pons, right or left midbrain, left prosencephalon.

Now, we start to clump things. Well, for starters any animal with cerebellar disease is expected to have hypermetria and/or intention tremors and Maria did not. We can cross out cerebellar disease. What else? What is the one spot where all of the signs can be explained? That's right - medulla on the right! Voila, lesion localization. 

OPTION 2:
The other way to work through this is to identify the cranial nerve affected on the exam (in this case, cranial nerve 8), identify the brainstem segment associated with this cranial nerve (in this case, medulla) and then ask yourself if you can identify if she has a) paw replacement deficits b) hemiparesis and/or c) mentation changes. . If not, it is peripheral and if so, it is brainstem. 

Differential Diagnoses

Brain stem vestibular disease in an elderly dog without an important prior medical history would suggest the following differential diagnoses:
Degenerative: none
Anomalous: none
Metabolic: Hypothyroidism
Neoplastic/nutritional: Neoplasia of the brainstem
Infectious/inflammatory/idiopathic: meningoencephalitis (infectious or inflammatory)
Trauma: no supportive history
Vascular: Cerebrovascular accident (stroke)

Final diagnosis: cerebrovascular accident (stroke). 

Please reach out if you have a case that is troubling you, a client that needs reassurance that you're doing all you can, or simply have a question. I hope you have a great week!

Neuroanatomic Lesion Localization Practice book!

It's Here! The Small Animal Neuroanatomic Lesion Localization Practice Book by yours truly!

It's always hard to self promote, so instead I wish to draw your attention to the many neurologists that contributed cases that made this little workbook the workhorse that it is.
1. Dr. Helena Rylander (UW-VC neurologist)
2. Dr. Joy Delamaide-Gasper (MVS neurologist)
3. Dr. Kari Foss (U of I neurologist, and former student)
4. Dr. Devon Hague (U of I neurologist)
5. Dr. Julien Guevar (Swiss neurologist and former UW-VC Neurologist)
6. Dr. Susan Arnold (U of Minnesota Neurologist and UW- VC graduate)
7. Dr. Sam Long (Australian neurologist and all around amazing guy)
8. Dr. Simon Platt (Forum UGA neurologist and ACVIM-Neurology past president)

The Small Animal Neuroanatomic Lesion Localization Practice Book is just that - a practice book - geared for general practitioners, students, and interns who are interested in brushing up or dusting off their neuroanatomic lesion localization skills. This little ditty has 7 chapters, with many cases in each chapter for you to try your hand at neuroanatomic lesion localization.

Not enticed enough?? If you get stuck - you know the author of the book and can email me directly for help! (yay for connections!)

Still not enticed?? Check out this link to see more: https://www.cabidigitallibrary.org/doi/10.1079/9781789247947.0000
Cost $65 USD

Note: I don't get any notifications of who buys a book, but if you suddenly stop consulting I'll assume you bought the book and learned it all and no longer need me. I really should stop trying to teach myself out of a job.... :)

That's it for this week. Not a typical TidBit per se, but hopefully you don't mind so much. Thanks for reading!
Have a great week!