It’s time for another case! This time, we’re going to talk about cat eyes – it’s almost Halloween, right? This case was taken from a case report presented in Vet Record August 2024 (https://doi.org/10.1002/vrc2.956). I thought it was interesting, and quite similar to another case I worked with one of you on…with the exception that we haven’t made it to MRI yet.
Signalment: 12 year old MC DSH.
History: 3 month history of mydriasis, photophobia and avoidance of jumping.
On examination, the cat had an unremarkable PE. Neurologic exam was as follows:
Mentation: normal
CN: Dilated pupils OU, no PLR (direct or indirect) OU, remainder normal. (Yes, even oculocephalic reflex!)
Gait: normal
Reflexes: not reported but assumed normal.
Postural reactions: normal
Lesion localization?
Let’s take a step back and remember that the parasympathetic innervation to the eye comes from midbrain (Parasympathetic nuclei of CN III), piggybacks with CN III to the eye where it then enters the iris muscles, causing constriction (normally). A lesion in the brainstem (midbrain in this case) should produce a change in mentation, paw replacement deficits, and/or hemiparesis along with the CN deficit. Bilateral peripheral parasympathetic damage hadn't been reported yet, but it would stand to reason that damage to CN III should result in strabismus and a loss of oculocephalic reflex (physiologic nystagmus). These somatic changes would/should be in conjunction with the parasympathetic changes expected.
This case was localized to bilateral peripheral parasympathetic nerves because there wasn’t evidence of a brainstem lesion. This is reasonable!
MRI and CSF, along with bloodwork were normal. Unfortunately, they could not collect enough blood for infectious disease testing. Based on these findings, the cat was diagnosed with an idiopathic bilateral peripheral neuropathy of the parasympathetic nerves. So cool! No signs of progression have been noted over 9 months.
I hope you enjoyed reading about this interesting case report. If you have any questions about the lesion localization, or anything else, please let me know! Have a great week!