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Teaching NeuroImages: Hypertrophic olivary degeneration in a young man with POLG gene mutation

A 30-year-old man with sensorineural hearing loss presented with subacute somnolence, slurred speech, and unsteady gait following treatment with peginterferon α-2b and ribavirin for chronic hepatitis C virus. Examination revealed scanning speech, horizontal nystagmus, gait ataxia, and symmetric hyporeflexia with distal sensory loss. There was no palatal myoclonus. Metabolic and serologic workup and blood lactate were unrevealing. Brain MRI demonstrated bilateral hypertrophic olivary degeneration (HOD, figure). Whole exome sequencing identified a homozygous pathogenic p.W748S POLG mutation.1 Differential diagnosis of bilateral HOD includes mutations in the nuclear genes crucial to mitochondrial function, POLG and SURF1.2