A 28-year-old man with sickle cell disease presented with 7 months of difficulty walking. Initial examination 3 months prior to admission to our hospital was thought to be consistent with a polyneuropathy. He was areflexic, was unable to stand on toes or heels with decreased sensation on the left foot to light touch and vibration, had difficulty with heel to shin, and was unable to perform tandem gait. Laboratory tests revealed anemia (hemoglobin 7.2 g/dL) and elevated creatinine (1.49 g/dL). HIV, antinuclear antibodies, antineutrophil cytoplasmic antibodies, hepatitis serologies, rapid plasma reagin, thyroid-stimulating hormone, copper, SSA/B, and Lyme titers were unremarkable. B 12 deficiency (B 12 188 pg/mL) and a mildly elevated erythrocyte sedimentation rate (ESR) at 24 mm/hour were found. Initial MRI brain showed multiple foci of fluid-attenuated inversion recovery hyperintense lesions in the subcortical and periventricular white matter. Lesions did not restrict on diffusion-weighted imaging (DWI); however, a few lesions demonstrated enhancement with gadolinium. MRI of the spine was unremarkable. Lumbar puncture (LP) was remarkable for a CSF protein of 144 mg/dL, leukocytes 43/mL (92% lymphocytes), erythrocytes 2,400/mL, and glucose 41 mg/dL. There were no oligoclonal bands. The patient was treated with IM injections of B 12 , without improvement in his deficits.Questions for consideration: