Could the Immune System Play a Role in Some Cat Seizures?
Seizures in cats are frightening to witness and can be hard to explain. In many cases, vets run infectious disease tests and brain scans and still come up empty. A new case report published in Frontiers in Veterinary Science describes one juvenile cat whose unexplained seizures occurred alongside antibodies against a brain receptor. Antibodies are proteins the immune system normally makes against infections, but they are sometimes found directed at the body’s own tissues. Over the following weeks, seizure control improved and the antibody level fell.
This is a single case, and the findings are an observed association only. The report does not show that the antibodies caused the seizures, and the authors say an incidental finding cannot be ruled out. But it raises a question worth studying: might antibodies like these be relevant in some cats with unexplained seizures?
Why Seizures in Cats Are Sometimes a Mystery
A seizure happens when the brain’s electrical signals fire in a sudden, uncontrolled burst. In cats, seizures can have many causes — viral infections, toxins, tumors, or structural brain changes. Vets use a combination of blood tests, infectious disease screening, and MRI scans to look for those causes.
But sometimes all of those tests come back normal. This is called “idiopathic” epilepsy — meaning the cause is simply unknown. That situation is frustrating for both owners and vets, because without knowing the cause, it’s harder to choose the best treatment.
In humans and dogs, researchers have described conditions in which the immune system appears to target proteins on brain cells, and seizures can be part of the picture. This is called autoimmune encephalitis. How often something similar occurs in cats is not known.
What Happened in This Case
Veterinary researchers described one juvenile cat that was having seizures. Standard testing was done first — infectious disease screening and an MRI — and nothing definitive turned up to explain the episodes.
That’s when the team looked for something less commonly tested: antibodies directed at a specific brain receptor called mGluR1. Short for metabotropic glutamate receptor 1, it is a protein on brain cells that helps regulate how nerve signals are sent. Think of mGluR1 like a volume knob for brain activity. Whether the antibodies found in this cat had any effect on that knob was not tested, and the report does not establish that they interfered with it.
The cat’s serum (the liquid part of the blood) tested positive for mGluR1 antibodies at a titer of 1:80 — a titer is simply a measure of how much of a specific antibody is present. Importantly, that positive result came from a single method: a cell-based assay designed for human samples. Testing of the cat’s cerebrospinal fluid (the fluid around the brain and spinal cord) was negative, and a separate tissue-based assay was also negative.
The Two Key Observations
Antibodies Turned Up When Everything Else Was Normal
The notable part of this case is that the antibodies were found after other, more common causes had been looked for. The infectious disease workup and MRI were unrevealing — meaning routine explanations didn’t apply — and this type of antibody had not previously been reported in a cat with seizures.
The finding comes with real caveats. The positive result was serum-only, on a human cell-based assay, and was not corroborated by the cerebrospinal fluid or tissue-based testing. No brain tissue examination was available to confirm inflammation, and the authors explicitly note that incidental seropositivity — antibodies present without causing disease — cannot be excluded.
Seizure Control Improved While the Antibody Titer Fell
Over roughly four weeks of follow-up, the cat’s seizure control improved and the antibody titer fell. That sounds suggestive, but the two changes cannot be separated from the treatment the cat received during the same period.
The cat’s antiseizure medication was changed: phenobarbital was reduced and levetiracetam was added. No immunosuppressive therapy — the kind of treatment used when an immune attack is being targeted — was given at any point. The authors state that the clinical improvement may primarily reflect the optimized antiseizure treatment rather than any change in the antibodies, and that the antibodies’ direct role could not be assessed. Four weeks is also a short window from which to draw conclusions about a seizure disorder.
What This Could Mean for Cats With Seizures
A Narrow Question to Raise With Your Vet
The authors suggest that mGluR1 antibody testing could be considered in one specific situation. That is a cat whose seizures do not respond to antiseizure medication and who also has concurrent behavioral abnormalities, once routine investigations have been inconclusive. That is a much narrower group than “cats with seizures.”
Outside of that situation, this single case does not support adding antibody testing to a seizure workup. Testing for brain-related antibodies is not established in cats, the assays used here were developed for human samples, and a positive result would not, on its own, explain a cat’s seizures.
Signs to Watch For and When to Seek Veterinary Care
If your cat has a seizure — especially for the first time — contact a veterinarian promptly. Signs of a seizure in cats can include:
- Sudden collapse or loss of balance
- Uncontrolled muscle twitching or jerking
- Drooling, paddling of the legs, or loss of bladder control
- A period of confusion or disorientation afterward (sometimes called the “post-ictal” phase)
After a seizure, your vet will decide which tests are appropriate, which commonly include blood work, infectious disease testing, and sometimes an MRI. A veterinary neurologist is the specialist best equipped to evaluate seizures that stay unexplained. Any decisions about testing or medication belong with your veterinary team.
Limitations of This Research
It is essential to keep the scope of this report in perspective. This is a report of one single cat, and its design cannot establish cause and effect.
The specific limits matter here. The antibody result was positive in serum only, at a low titer, using an assay built for human samples, while cerebrospinal fluid and tissue-based testing were negative. No histopathologic confirmation was available, and incidental seropositivity could not be excluded. The cat received no immunosuppressive therapy, so the antibodies’ pathogenic role was never tested, and follow-up lasted only four weeks. A single case also cannot tell us how common these antibodies are in cats, with or without seizures.
The authors acknowledge these limits. The value of the report is in describing a finding that had not been recorded in cats before and giving other researchers something specific to investigate.
The Bottom Line
One juvenile cat with unexplained seizures tested positive in serum for antibodies against the brain receptor mGluR1, and its seizure control improved while the antibody titer fell over four weeks. That is an association in a single animal, not a demonstrated cause. The positive result was not confirmed by cerebrospinal fluid or tissue-based testing, and no immunosuppressive treatment was used. The improvement may simply reflect the adjusted antiseizure medication given at the same time.
For cat owners, the practical takeaway is unchanged: report any seizures to your veterinarian right away, and work through the standard diagnostic steps they recommend. This report is a starting point for researchers, not a new test to ask for.
This article summarizes peer-reviewed research for educational purposes. Always consult with your veterinarian for personalized advice about your pet’s health and behavior.