Charcot-Marie-Tooth (CMT) disease is a hereditary motor and sensory neuropathy characterized by similar phenotype despite genetic heterogeneity 1 . Charcot-Marie-Tooth type 1A, linked to a~1.4 Mb duplication containing the peripheral myelin protein-22 gene on chromosome 17p11.2, accounts for~50% of all CMT patients [2][3][4][5][6] . Disease severity varies considerably in CMT1A, however, the prototypical phenotype involves weakness and atrophy of distal limb muscles, distal sensory deficits and diminished deep tendon reflexes with symptoms appearing in childhood 7 . Interestingly, increased motor and sensory impairment is observed in CMT1A patients with diabetes 8 . Pes cavus, a skeletal deformity resulting from characteristic sparing of foot plantar flexors in combination with early weakness of dorsiflexors, is observed in approximately twothirds of CMT1A patients 7 . In contrast, mutilating foot deformities resulting from prominent distal sensory deficits are not typical of CMT1A, but have been associated with the 2B subtype of CMT disease and can be a feature of the Hereditary Sensory Neuropathies 9 . We present a patient who developed Charcot ankle, a destructive arthritis associated with peripheral sensory neuropathy, as a result of CMT1A augmented by type II diabetes mellitus.
CASEThis 49-year-old man with type II diabetes mellitus for ten years was initially assessed by neurology for a benign headache. He was noted on examination to have classical findings of CMT disease, though he was unaware of the diagnosis. The patient had bilateral pes cavus and walked with a mild steppage gait, being able to clear his toes when walking without ankle splints. Moderate bilateral weakness of ankle dorsiflexion and eversion was accompanied by diminished patellar and absent Achilles reflexes. Sensory examination revealed diminished proprioception, vibration sense, and pin-prick perception distal to the ankle. The patient recalled experiencing numbness and deformity of both feet since early childhood. In addition, several family members (two maternal uncles, one brother and one maternal nephew) had been diagnosed with CMT disease. His mother had high foot arches, but had not been assessed for CMT.Motor nerve conduction studies performed on the left median and ulnar nerves revealed a markedly diminished conduction velocity (18.2 m/s; normal >40.0 m/s) and reduced compound muscle action potentials (3.3 and 2.8 mV, respectively; normals > 4.0 and 6.0 mV). No conduction block was present. No response was elicited following motor nerve conduction studies performed on the left tibial and peroneal nerves (recording over foot muscles) or sensory recordings of the left ulnar, median, and THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES 419