Riddle me this: a 10 month old cat is brought into your exam room by a very concerned owner. They report that the cat has had a rapid, progressive weakness develop over the past 2 weeks. Being the astute veterinarian that you are, you notice that the cat takes 3-4 steps and then sits. There doesn't appear to be any ataxia...just paresis (weakness).
Neurologic examination:
Mentation: BAR
Cranial nerves: all normal (about 11% of cats will have facial nerve paralysis with this disease)
Gait: Ambulatory tetraparesis, worse in the pelvic limbs
Reflexes: reduced withdrawal all limbs, absent patellar reflexes bilaterally.
Postural reactions: reduced to absent tactile placing in both pelvic limbs, reduced tactile placing in both thoracic limbs.
Palpation: non-painful
The remainder of the physical examination is unremarkable.
What is the neuroanatomic lesion localization?
Start at the very beginning. Are there any signs of seizures, mentation changes or cranial nerve deficits? No. Therefore this cannot be intracranial lesion localization. We have all four limbs affected therefore if this is a spinal neuroanatomic lesion localization it must be cranial to the front legs. This means C1-C5 or C6-T2 myelopathy. (If the lesion was T3-L3 or L4-S3, the thoracic limbs should be normal.) To narrow it down between C1-C5 or C6-T2, we look at reflexes. Reflexes are reduced in the thoracic limbs therefore this would suggest a C6-T2 myelopathy. BUT WAIT!! The reflexes in the pelvic limb are also reduced to absent and that cannot happen with a C6-T2 spinal cord lesion. The reflexes in the pelvic limbs should be normal with a C6-T2 spinal cord lesion. Is this a multifocal lesion, affecting two spinal cord segements (C6-T2 and L4-S3)? Although possible, you would expect a proprioceptive ataxia with a spinal cord lesion therefore this is very unlikely to be a spinal cord lesion at all, even a multifocal spinal cord lesion. There, we must assume this is not spinal cord or intracranial lesion. What does that leave us? Neuromuscular disease, that's right! Your options are: 1) peripheral nerve, 2) neuromuscular junction or 3) muscle. Animals with muscle disease should have normal reflexes (and do, except with myasthenia gravis), so it isn't that. This is either a neuromuscular or peripheral neuropathy localization.
Our differential diagnosis would include diseases such as: toxoplasma or fungal neuropathy, myasthenia gravis (yes, I know this localizes to the muscle but clinical signs look like a junctionopathy at times!), and immune mediated neuropathy.
Diagnostic testing for this patient
CBC, serum biochemistry (including CK!) is normal. Toxoplasma testing was negative, as is the myasthenia gravis titer. Occasionally we will see an elevated CSF WBC or protein count with this mystery disease, but it isn't common.
Muscle and nerve biopsy results
Diffuse variability in muscle fiber size is expected on biopsy. Nerves are almost all missing from the muscle biopsy sections. The nerve biopsy is markedly abnormal, with inflammatory cells infiltrating the axon, nodes of Ranvier and Schwann cells.
Diagnosis: Immune mediated polyneuropathy!
This is a very interesting disease for many reasons but most notably, most cats can achieve a complete recovery without any treatment at all. In a recent study (see below), 10/11 cats that received no treatment obtained full recovery with a median time of 4 weeks. Nine of 12 cats that received glucocorticoids and 18/20 cats that received L-carnitine supplementation recovered as well. Relapses are reported and can occur months or years after resolution of signs. Overall, all except 1 cat improved regardless of treatment in this study. This same study found a predominance in males but did not find a breed association.
So there you go! A self resolving, relapsing remitting polyneuropathy of young cats.
Article: DOI: 10.1111/jvim.16701
I hope you have a great week and look forward to working with you soon!