Very late-onset MOG-IgG-associated longitudinally extensive myelitis in a 79-year-old man: a case report

Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is a distinct inflammatory demyelinating disorder that can occur across the lifespan. Although late adult-onset MOGAD, commonly defined as onset at ≥ 50 years, is increasingly recognised, very late-onset disease beginning at ≥ 70 years remains uncommon and may pose substantial diagnostic challenges because neoplastic, vascular, degenerative, and radiation-related causes are often prioritised in this age group. We report a 79-year-old man with a one-year history of progressive gait disturbance and imbalance. His medical history included hypertension, diabetes mellitus, coronary artery disease, and rectal carcinoma treated with chemoradiotherapy in 2007. Neurological examination revealed mild left lower-limb weakness, hyperreflexia, bilateral Babinski signs, a T6–T10 sensory level, and broad-based gait. Cerebrospinal fluid analysis demonstrated mild pleocytosis (28 cells/µL, 85% lymphocytes), with a glucose level of 68 mg/dL and a protein level of 42 mg/dL. Cerebrospinal fluid cytological examination was negative for malignant cells. Serum testing was negative for aquaporin-4 antibodies but positive for MOG-IgG, detected at a titer of 1:100 using a fixed cell-based assay. MOG-IgG testing was not repeated during follow-up, and confirmation with a live cell-based assay was not available. Spinal MRI demonstrated a longitudinally extensive expansile T2-hyperintense lesion extending from T6 to T10 with focal cord atrophy in the rostral segment. Somatosensory evoked potentials showed bilateral conduction slowing within the gracile fasciculus pathways. The patient received intravenous methylprednisolone followed by oral prednisolone and azathioprine; azathioprine was discontinued due to lymphopenia and thrombocytopenia. At the three-month follow-up, his Expanded Disability Status Scale score had improved from 4.0 to 3.0, accompanied by marked radiological regression of the spinal cord lesion. He subsequently remained clinically stable on oral prednisolone 10 mg/day, without relapses or further progression over four years. This case demonstrates that MOGAD should remain in the differential diagnosis of longitudinally extensive myelitis even in very elderly patients. In atypically progressive presentations, MOG-IgG results should be interpreted within the complete clinical and radiological context while structural, neoplastic, vascular, and radiation-related mimickers are carefully investigated. Treatment should be individualized according to comorbidities, relapse risk, and tolerability.