Clinical Reasoning: A patient with rapidly progressive sensory loss and imbalance.

SECTION 1 A 52-year-old man presented with sudden onset of acral paresthesia and imbalance. The patient did not have any recent illness, sick contacts, or travel abroad. He denied weakness, pain, bowel or bladder incontinence, dysphagia, dysarthria, or shortness of breath. On neurologic examination, 1 month into his symptoms, he had reduced muscle strength in his finger spread, extension, and flexion on both sides graded on Medical Research Council scale 42/5 and in toe extensors 24/24 and toe flexors 24/4. The rest of his muscle strength was normal. Reflexes were absent throughout. He had reduced sensation to all modalities in a length-dependent pattern up to his midshin and wrists on both sides. He was severely unsteady when walking and he could not tandem. Romberg was positive. The rest of his neurologic examination was normal apart from high arches and hammertoes. The patient had a family history of Charcot-Marie-Tooth disease type 1A (CMT1A) (PMP22 duplication) and was himself tested, although asymptomatic, and was also found to be carrying the mutation.