To share an atypical presentation of Myelin Oligodendrocyte Glycoprotein Antibody-Associated disease (MOGAD) with unusual age of onset and radiolographic findings.

MOGAD encompasses a spectrum of autoimmune disorders known for central nervous system (CNS) inflammation and demyelination, typically affecting younger populations. Recent literature reveals that MOG antibody disease can manifest in diverse clinical forms. While typical MOGAD presentations involve inflammation and demyelination, rare cases of isolated encephalitis have emerged, particularly in elderly individuals. This case details an 80-year-old male with radiographic negative MOG antibody encephalitis.

An 80-year-old male with pre-existing mild cognitive impairment developed a one-week history of progressive cognitive decline and a seizure episode. Neurological examination revealed impaired higher cognitive functions (orientation, concentration, and delayed recall) without focal deficits. There were no signs of meningeal irritation; however, the patient had a fever without leukocytosis. Empirical antibiotic treatment was initiated, and cerebrospinal fluid (CSF) was collected nine days later. The analysis revealed pleocytosis (6 white blood cells), elevated protein levels (147 mg/dL), a positive MOG antibody titer (1:320), and the presence of two oligoclonal bands, suggesting CNS inflammation. All infectious and autoimmune encephalitis panels returned negative results. Brain and cervical spine imaging did not show evidence of acute inflammation or demyelination. Due to the lack of improvement with empirical therapy, the patient was started on intravenous immunoglobulin (IVIG) for suspected atypical MOG antibody-related encephalitis. Treatment efficacy was assessed using the Mini Mental Status Exam (MMSE). The MMSE score improved from 13/30 on the second day of IVIG to 21/30 before discharge, and the repeat MOG antibody titer reduced to 1:80.

This case highlights the diverse clinical spectrum of MOGAD, demonstrating its potential to cause encephalitis in elderly individuals, deviating from the typical MOGAD pattern. It emphasizes the importance of promptly recognizing MOG antibody encephalitis to reduce associated mortality and morbidity.