Tumefactive demyelination as the first presentation of MOG ab-associated disease.

Tumefactive demyelination is a rare but clinically significant manifestation of myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), often posing diagnostic challenges due to its resemblance to neoplastic lesions. We report a case of a 45-year-old woman presenting with a 3-week history of limb weakness, slowed responsiveness, and aphasia. Neurological examination revealed confusion and sensory aphasia. Serum MOG antibody was positive at a titer of 1:320, while AQP4 and GFAP antibodies were negative. Cerebrospinal fluid (CSF) analysis showed a positive MOG antibody titer of 1:1. Brain MRI demonstrated a left frontal lobe mass with surrounding edema and patchy contrast enhancement. Brain biopsy revealed perivascular lymphocyte cuffing, focal myelin loss, and preserved axonal integrity, consistent with tumefactive demyelination. PET-CT revealed heterogeneous 11C-methionine (MET) and 18F-fluorodeoxyglucose (FDG) uptake, with an L/W of 3.1 and L/W of 2.6, supporting a possible demyelinating process. The patient was diagnosed with MOGAD and treated with intravenous methylprednisolone (IVMP), resulting in complete symptom remission and significant lesion reduction on follow-up MRI. Tocilizumab was initiated for relapse prevention, and serum MOG antibody titers decreased from 1:320 to 1:100 over nine months. This case highlights the importance of integrating clinical, radiological, and pathological findings to differentiate tumefactive demyelination from neoplastic lesions. Early diagnosis and treatment are crucial for favorable outcomes in MOGAD-associated tumefactive demyelination.