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Autoimmune encephalitis prevalence has risen notably in recent years, driven by advancements in neuronal antibody research. AE is the most common form of encephalitis of non-infectious origin, and it has a wide spectrum of clinical phenotypes. However, it remains a rare autoimmune disease frequently underdiagnosed. This report elucidates the diagnostic complexities, therapeutic challenges, and the possibility of relapse regarding the rare phenomenon of co-expression of Anti-GAD65 and Anti-NMDA autoimmune encephalitis.

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We present a case report of an 18-year-old female who presented to the hospital with a biparietal subacute headache that progressed with paresthesias and behavioral changes like mutism, inattention, hypersomnia, and myoclonus. Her physical examination revealed mixed dysarthric speech (flaccid and spelled), dyscalculia, and altered abstraction. She underwent an electroencephalogram that showed the presence of mild generalized dysfunction, without epileptiform activity. Imaging studies and a lumbar puncture did not support the diagnosis of infectious pathology. The Bush Francis score was rated 1 and a MOCA test 17, revealing cognitive impairment. Anti-NMDA and Anti-GAD65 antibodies were reported in the cerebrospinal fluid autoantibodies panel. She started treatment with methylprednisolone plus sessions of plasmapheresis, which finally showed improvement and she was discharged, but within less than two months she had a relapse of neuropsychiatric symptoms and was admitted again. Thus rituximab treatment was initiated as a second-line option that resulted in good clinical evolution and no signs of relapse in the following 2 months.  

This case underlines the complexities of management in AE, particularly when confronted with co-expression antibody positivity. Clinicians should maintain a high index of suspicion, particularly in underrepresented populations, and consider the need for long-term assessment alongside optimal immunotherapy, keeping in mind its therapeutic nuances. Future research directions are needed, to enhance our comprehension of AE pathogenesis, optimize treatment strategies, and address disparities in diagnosis across diverse demographics.