A 57-year-old man with deteriorating mobility and deafness

A 57-year-old man re-presented to the neurology clinic in August 2014 with a 20-year history of progressive gait decline, and a 2-year history of requiring crutches and a wheelchair. Recently, he had also developed numbness below his knees. His upper limb function had remained normal. His hearing had declined over the years and he now wore bilateral hearing aids for sensorineural deafness. He had a 10-year history of red–green colour blindness and a 5-year history of central vision distortion. He had a several year history of bladder dysfunction with increased frequency, urgency of micturition and incomplete bladder emptying. His only medication was simvastatin 20 mg daily for hypercholesterolaemia. His neurological symptoms had been previously investigated but without a diagnosis, and he had been lost to follow-up for several years. On examination, he had a narrow-based stiff-legged gait. Ophthalmic assessment identified healthy posterior poles apart from epiretinal membranes and bitemporal optic disc head pallor. He had red–green colour blindness, with visual acuities of 6/12 right and 6/7.5 left. There was gaze-evoked nystagmus and bilateral sensorineural deafness. He had bilateral lower limb hypertonia with sustained ankle clonus, pyramidal weakness, hyper-reflexia and extensor plantar responses. Pinprick and vibration sense were impaired below the knees bilaterally and subtle dysdiadochokinesia in the upper limbs. On neuropsychology assessment, he showed stable mood and intact cognition. ### Question 1 What other history you would like to know? Family history might be informative. His father died aged 53 of myocardial infarction and was reportedly hard of hearing. His mother died aged 63. He is an only child and with no history of consanguinity. He has two daughters, aged 30 and 32, and his eldest daughter has two children; all of them are well. There are no neurological diseases in his second-degree relatives. ### Question 2 What is the differential diagnosis? The presentation is that of …