About 8 months after the gradual onset of subtle gait ataxia, unstable bicycle riding and slurring of speech under stressful circumstances, a woman in her mid 40s underwent MRI which was assessed as normal (fig 1A). She was referred for a second opinion to our hospital with mild gait ataxia, slight interruptions in the fluency of high speed articulation and small saccades during ocular pursuit. Follow-up MRI was normal (fig 1B) although in retrospect a slight signal increase in the left …