A 62-year-old right-handed woman was referred from ophthalmology in 2009, with a 5-year history of episodic and then more persistent balance difficulty. This was particularly noticeable during tasks requiring depth perception, such as walking down stairs, in the dark and when walking on uneven surfaces. She reported visual ‘bobbing’ when walking, with occasional vertigo, particularly following sudden head movements. As her unsteadiness progressed, she developed double vision on horizontal gaze, with the false image appearing askew (both horizontal and vertical separation). This was most noticeable during tasks requiring fast-tracking eye movements, such as scanning supermarket shelves.

By early 2008, she had a ‘droopy’ left eyelid, worse in the evenings but with no limb weakness or difficulty with swallow or speech. Over the years, she developed left arm clumsiness and ‘slowing’ of movements. She now needed a walking stick for support. There was no weight loss, difficulty with hearing or tinnitus.

She took treatment for hypertension and hypercholesterolaemia: her medications included bisoprolol, aspirin and atorvastatin. Eight years earlier, she had a melanoma removed from her left thigh. As a child, she had recurrent urinary tract infections complicated by pyelonephritis and requiring intravenous antibiotics; it was unclear as to whether she received aminoglycoside antibiotics. She did not smoke cigarettes and drank minimal alcohol.

Her mother had died in her fifties from myocardial infarction and father had died in his fifties from complications of rheumatic heart disease. Her mother had suffered frequent debilitating headaches, diagnosed as migraines by a neurologist. She was one of twins, but her male co-twin died aged 36 h from unknown cause. A second brother, who also had migraine, died aged 54 years from myocardial infarction. She had two healthy children aged 38 and 36 years.

On examination, there was no evidence of autonomic involvement. Her cognition was normal, with congruent mood. …