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.

Predicting Spinal Shock

When things go bump in the spine...

So many interesting cases happened this past week! Please join me today as we evaluate a 4 year old FS Mixed breed 10 kg dog, together. Her presenting complaint was acute onset difficulty walking in the last 24 hours.

Neurologic Examination:
Mentation: BAR
Cranial nerves: all normall
Gait: Paraplegia (no voluntary movement)
Reflexes: reduced withdrawal in both pelvic limbs, poor anal tone, and reduced cutaneous trunci reflex to T13 bilaterally. All remaining reflexes normal.
Postural reactions: Absent both pelvic limbs, normal both thoracic limbs
Palpation: Painful at T12-T13, remainder non painful.
Other: Absent nociception in both medial and lateral toes of both pelvic limbs.

Neuroanatomic lesion localization: Hmmmm....let's take a moment and think this through.
1) Does this dog have neurologic disease? Yes!
2) Are forelimbs and intracranial structures normal? I'd say, yes. Okay, the lesion is caudal to T2.
3) Our choices for lesion localization are, T3-L3, L4-S3 or neuromuscular at this point.
4) Are reflexes affected? Yes. Therefore the lesion must be L4-S3 or neuromuscular. But wait! What about that back pain and reduced c. trunci reflex? The cutaneous trunci reflex reflects a T3-L3 myelopathy and the back pain certainly supports that but could be from non-neural causes. Is this multifocal spinal cord?
5) Hold the phone, Barnes. Tell me why this isn't neuromuscular? Okay, I'll tell you. Sensory neuropathies are extremely rare and are usually congenital. Therefore, to have a loss of deep pain this animal needs to have a spinal cord lesion. Moving on then....

Neuroanatomic Lesion localization: Folks, this is an example of multifocal neuroanatomic lesion localization of T3-L3 and L4-S3 spinal cord. Primary differentials would include acute diseases affecting the spinal cord (such as FCE, disc herniation, trauma) plus spinal shock, or a true multifocal spinal cord disease (such as meningomyelitis).

What is Spinal Shock?

Spinal shock occurs when there is "reverberation" and a change of the local environment that results in temporary cessation of reflexes downstream from the injury. In most models, the injury is at the TL junction so the pelvic limb spinal reflexes are temporarily lost. This is transient! For most animals, the reflexes return in 1-3 days if not shorter. It is important to note that there is NO pathology in the pelvic plexus.

Predictive Models

How do you know when you have a pet with spinal shock or a pet with a multifocal disease when you have multifocal spinal cord lesion localization? The honest truth is you don't know until you do an MRI and show that only one lesion is present. However, there was a predictive model recently published (https://onlinelibrary.wiley.com/doi/10.1111/jvim.16352) that showed smaller breeds, with a history of less than 24 hours, are more likely to have spinal shock. As with all predictive models, this isn't fool proof, but it is a start. For the case above, I would strongly consider spinal shock with a T3-L3 myelopathy. Indeed this is what we had; we had an FCE at T12-L1 on MRI and no additional lesions in the L4-S3 segment.

Hope this TidBit was helpful to your practice! Please reach out if you have a case I can help with, or if you have an idea for a TidBit Tuesday mailer. Happy February!