Autoimmune encephalitis is a unique pathology, identified in perhaps up to 50% of humans with encephalitis, and recently identified in a large cohort of cats. In a study published in Vet Journal (2023), Glantschnigg-Eisl et al described the clinical, laboratory, radiological and pathological findings in 32 cats diagnosed with this specific form of epilepsy. Human autoimmune epilepsy is caused by immune attack of the voltage-gated potassium channel (VGKC), generating specific antibodies to this protein complex and the secreted protein LGI1 as well. It is now proposed that the presence of these antibodies reflect a specific form of limbic epilepsy in cats, similar to the autoimmune epilepsy noted in humans. Most importantly to us (veterinarians), cats with this form of epilepsy have a normal MRI and CSF analysis! Therefore, calling it encephalitis based on our standard testing is challenging. Is it a form of idiopathic epilepsy, or an encephalitis? Time shall tell. The authors describe this as an encephalitis, similarly to the human counterpoint. Below is a small summary of their findings. For the full study, please refer to the article link at the bottom.
Clinical Picture
All cats in the study had seizures as their presenting complaint. All cats had positive antibodies to VGKC, with 26 cats having LGI1 antibodies as well. No clinical findings distinguished cats with LGI1 antibodies from those without. Focal and generalized seizures were almost evenly divided as a presenting seizure type with cluster seiuzres in 27/32 cats. Similar to humans with limbic epilepsy, many of the cats (22/32) had interictal behavior changes with a history of unprovoked aggression in 12/32 cats. This was identified as a common finding but not yet pathognomonic for this form of epilepsy. Median age at onset was 3.42 years.
Laboratory Findings
.No significant laboratory abnormalities were identified. As noted above, CSF analysis was normal for all but 1 cat and that cat had only a mildly elevated protein.
Long-term Outcome
Phenobarbital was started in 26/28 cats that underwent treatment with about 1/2 of the cats having a second AED added throughout treatment. Prednisone was administered in 10/32 cats (most of which were the LGI1 positive cats).The cats that received steroids, often received prednisone. This medication was administered to the cats with the most severe neurologic signs, including seizure frequency or severity, and was linked to poorer survival. As the authors noted, it is unclear if the prednisone is linked with poorer outcome or if the survival is linked to more severe condition and therefore prognosis. This was interesting because the human seizure disorder associated with LGI1 antibodies is typically rapidly and markedly responsive to steroids.
Two factors were associated with prognosis in this study. The first was number of seizures at presentation. Cats with a higher seizure frequency were more likely to be euthanized. The second was the association with hippocampal pathology. Higher MRI scores suggested a lower prognosis and higher likelihood of euthanasia. The overall survival rate was 70-80%, which was similar to survival rates for idiopathic epilepsy in cats. At 1 year, most cats had a marked decrease in seizure activity from a mean of 3.6 seizures daily to 1-2 per year. This suggests that if they survive the short term, their long-term prognosis is good. QoL scores were good to acceptable in the long-term follow-up group.
What are my take away points from this study for practice?
1. Be aware that this disease exists. If you see cats with seizures, especially severe onset seizures, VGKC autoantibodies could be an underlying cause.
2. Treat with phenobarbital - it works terrifically for most cats, regardless of the underlying cause.
3. Steroids may not be the answer. Then again, maybe they are if we catch the disease earlier?? I don't think we can make this a take away just yet; more information is needed.
I hope you have a wonderful week and thanks for reading!
A gentle reminder: I've had an uptick in cancelations over the past few days. I know my schedule is getting booked out further than is typical, and I apologize for the resulting delay. Please cancel your appointments with as much notice as possible, whenever possible. I have a waitlist and would LOVE to move folks forward if I have an opening. I am hopeful that the waitlist will diminish soon now that I able to open up a few more days for consults. Thank you!
Lastly, gut yantif to those of you celebrating! I hope you had a safe fast yesterday.
Reference: https://www.sciencedirect.com/science/article/pii/S1090023323000254