The “H sign” in MOGAD myelitis

A 40-year-old man presented with acute urinary retention and bilateral lower limb weakness. MRI revealed a longitudinally extensive T2 hyperintense spinal cord lesion from C6 to T10, predominantly involving the gray matter ("H sign"). Brain MRI and CSF studies were unremarkable. Serum MOG-IgG was positive. The patient was treated with intravenous corticosteroids, with subsequent clinical and radiologic improvement. The imaging and clinical findings were consistent with myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD).