A man in his 60s was evaluated for progressive myelopathy. His symptoms evolved insidiously over a year and included groin numbness, incomplete bladder emptying, and leg weakness. Examination revealed spastic paraparesis. Magnetic resonance imaging (MRI) of the cervical and thoracic spine demonstrated a T2 hyperintense lesion extending from T6 to the conus but no evidence of abnormal flow voids over the surface of the cord and no evidence of gadolinium enhancement. Magnetic resonance imaging of the brain was normal. His leg weakness worsened after walking and improved with rest. The following blood results were negative or normal: vitamin B12, copper, West Nile virus, human T-cell lymphotropic virus types 1 and 2 antibodies, human immunodeficiency virus antibodies, methylmalonic acid, Lyme serology, erythrocyte sedimentation rate, lupus panel, antineutrophil cytoplasmic antibody, and VDRL. A lumbar puncture revealed a normal profile aside from mildly elevated total protein (0.068 g/dL; range, 0.015-0.06 g/dL; to convert to grams per liter, multiply by 10.0); notable negative cerebrospinal fluid results included oligoclonal bands, IgG index and synthesis rate, neuromyelitis optica–IgG, paraneoplastic panel antibodies, angiotensin-converting enzyme, cryptococcal antigen, and cytology. An angiogram showed no evidence of arteriovenous malformation.