It's Monday morning, and your first case is presenting for "not walking well". Let's review some neuroanatomic lesion localization so you can be awesome on a Monday morning!
Signalment: 4 year old FS Labrador X
History: The dog was outside playing in the backyard last night when suddenly she yelped and fell over. The owners use this dog for sport as well as for a pet, so she is known to be a very stoic dog. Right away they worried about pain because she vocalized. It was apparent that she couldn't walk back into the house, so they put her on a blanket and carried her inside. She was able to stand up but couldn't use her right front or right rear leg normally. They gave her dinner (which she ate) and allowed her to rest until the visit today. (Why didn't they take her to ER? I don't know...I'm just the neurologist!)
Physical examination on presentation was unremarkable. (Yes, you examined her stifles, and they appear stable).
Neurologic examination:
Mentation: BAR, very excited to see you (she's very excited to see EVERYONE)
Cranial nerves: all normal (high five for doing a full cranial nerve exam!)
Gait: She has an ambulatory right hemiparesis, with frequent falling to the right. She is able to walk 5-6 steps, unassisted, before falling or having her right limbs slide out. Note, the definition of ambulatory is the ability to walk a minimum of 5 unassisted steps IN ALL LIMBS.
Reflexes: No withdrawal reflex in the right front leg, absent bicep and triceps reflexes right front leg. The reflexes are normal in all other limbs
Postural reactions: Absent paw replacement right front leg a right rear leg. Normal paw replacement in both left front and left pelvic limb.
Palpation: No signs of pain on palpation or cervical ROM.
Nociception: She has motor in all four limbs, so you do NOT need to test nociception (deep pain)
Neuroanatomic lesion localization: Right C6-T2 myelopathy (spinal cord)
Why? We know the dog is mentally normal and has normal cranial nerves. She does not have a seizure history therefore there is no evidence of intracranial disease. You can cross that body part off. Therefore, the lesion must be caudal to the foramen magnum. A forelimb AND pelvic limb are affected which means this lesion must be cranial to T3. If the lesion was caudal to T3, only a pelvic limb, or limbs, should be affected. That narrows our window of concern to C1-T2, correct? From there, you need to evaluate the reflexes. If they are normal, the lesion is likely C1-C5 but in rare situations it is C6-T2. Normal reflexes aren't super useful to narrow this window further. However, she has reduced to absent reflexes in the right front leg. Reduced to absent reflexes suggest a lesion in the reflex arc itself, which is located C6-T2 in most dogs. Why did I say this was a spinal cord, not a peripheral nerve injury? If you guessed it was because the pelvic limb on the same side was affected you'd be correct! The long tracts (paw replacement testing, upper motor control) going to or from the pelvic limb must travel through the C6-T2 part of the spinal cord. If the dog has sustained damage to the spinal cord, the tracts to the pelvic limb should be affected. If the nerves to the front leg are damaged peripherally (i.e. with brachial plexus injury) the pelvic limb should be normal. You did it!
Differential diagnoses: This dog has an acute onset, non-painful spinal cord disease. I would include an FCE, AHNPE (acute hydrated nucleus pulposus extrusion) and possibly at Type I disc herniation on the top of my list. As we learned last week, we cannot ever take meningomyelitis off the list so that goes on the list, but lower. Lastly, although trauma wasn't witnessed, this was an acute onset disease, so trauma goes on the bottom of my list until proven absent.
We performed an MRI and diagnosed her with a suspected FCE. She entered rehab and supportive care and is doing well! With mobility and deep pain present, she is likely to make a good recovery but may not have completely normal mobility in the front right limb because the plexus was involved.
Did you enjoy this case? Did you find it difficult? Please let me know if have any topics or a lesion localization case that you wish I'd cover on a TidBit Tuesday. Have a great week!
The Five Types of Disc Herniation
The Five Types of Disc Herniation (that we know of!)
Dystrophic calcification secondary to chondroid degeneration of nucleus pulposus (NP), called a Hanson Type I. This causes mechanical stress on the outer annulus fibrosus (AF), leading to rupture of individual collagenous strands of AF and eventually full failure.
Fibrous degeneration occurs when fibers of disc split leading to accumulation of tissue fluid and plasma between them. Over time the mechanical pressure exerted by NP causes thickening of the AF dorsally, causing protrusion. (Hanson Type II).
ANNPE (Acute noncompressive nucleus pulposus extrusion) - this is normal NP that is exploded into the canal, usually during activity. Also called a traumatic disc herniation.
AHNPE (Acute hydrated nucleus pulposus extrusion) – An apparently normally hydrated NP that is compressive and often located ventral to the cord, often in the neck.
Significantly more neuro deficits and less signs of cervical pain with AHNPE compared to other causes of cervical myelopathy.
FCE (Fibrocartilaginous embolism): a piece of NP that becomes dislodged and finds its way into the vasculature surrounding the spinal cord. This can be into venous or arterial blood vessels. The end result is an acute shift in blood flow at the level of the spinal cord.
Match the clinical sign with the type of disc herniation
A. Chronic, progressive ataxia progressing to paresis
B. Acute, non-progressive unilateral weakness affecting one leg, or one side (hemiparesis)
C. Acute, progressive, painful ataxia progressing to paresis in a chondrodystrophic dog
D. Acute non-progressive ataxia and paresis affecting both sides of the body (paraparesis or tetraparesis)
E. Acute, rapidly progressive tetraparesis and ataxia of all four limbs with minimal cervical pain
If you answered...
Type I: C
Type II: A
ANNPE: D
AHNPE: E
FCE: B
you are correct!
Based on the clinical picture, it can be very difficult to distinguish Type I from ANNPE, and AHNPE. Typically, type I is painful (but not always), and the other two are minimally to non-painful.
Which of these require surgery?
Any disc herniation that results in compression of the spinal cord with associated clinical signs could be considered for surgical correction. This statement would then suggest that Type I, Type II and AHNPE could be surgically corrected. Therefore, any patient with signs of a progressive or painful myelopathy should be evaluated for diagnostic imaging (typically MRI) for possible surgical intervention whenever possible.
Bonus question:
Can you name two diseases that are commonly diagnosed instead of a type I or type II disc herniation? Scroll to the bottom for the answer!
Change is coming! Starting in September I will have new fees, and new availability. I am happy to accommodate outside of these hours whenever possible so please reach out if you cannot find a suitable time using the online scheduler. ( https://barnesveterinaryservices.com/ )
New Hours (Starting September 8th)
Monday 11a-1p, 4-5p
Tuesday 3-4p
Wednesday 11a-1p, 2-4p
Thursday 2-4p
Friday 12-1p
Saturday 9-11a
Bonus Question Answer
Meningoencephalomyelitis (a.k.a meningitis), and neoplasia. Keep these two on your differential diagnoses list when you suspect a disc herniation!!
