Seizures in a cat with metabotropic glutamate receptor 1 (mGluR1) antibodies: a case report

Autoimmune encephalitis associated with neuronal autoantibodies is increasingly recognized in veterinary medicine. In cats, previously reported antibodies have primarily targeted components of the voltage-gated potassium channel complex, such as leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2). Anti-metabotropic glutamate receptor 1 (mGluR1) antibodies are well described in human medicine but have not previously been reported in cats. A 5.5-month-old female domestic shorthair cat was presented for recurrent epileptic seizures and episodic behavioral abnormalities, including pica. Neurological examination revealed mild pelvic limb ataxia. Based on the history of epileptic seizures and behavioral abnormalities, the neuroanatomical localization was consistent with the forebrain. Magnetic Resonance Imaging (MRI) of the brain and cerebrospinal fluid (CSF) analysis were unremarkable. Infectious disease testing from CSF, including polymerase chain reaction (PCR) assays for Feline Coronavirus, Toxoplasma gondii, Feline Herpesvirus, and Rustrela virus, was negative. Neural antibody testing using tissue-based and cell-based assays identified an elevated serum mGluR1 antibody titer (1:80; reference <1:20), whereas cerebrospinal fluid and tissue-based assays were negative. Testing for other neuronal autoantibodies, including LGI1 and CASPR2, was negative. Following optimization of antiseizure therapy, the cat showed clinical improvement, accompanied by a decrease in the serum mGluR1 antibody titer. This report describes the first detection of mGluR1 antibodies in a cat with neurological disease and suggests a potential association between mGluR1 autoimmunity and epileptic seizures and episodic behavioral abnormalities in a cat.