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.