P13.1 Conduction block in Charcot–Marie–Tooth type 1B (CMT1B) neuropathy

Abstract

Background: On neurophysiological studies the hereditary demyelinating motor and sensory neuropathies (CMT1) usually show uniform reduction in motor conduction velocities. On the other hand, conduction block (CB) far from compression sites is typical of acquired demyelinating neuropathies. Aims: To describe a patient with CMT1 in whom neurophysiological studies disclosed marked CB outside entrapment sites. Case report:A34-year-oldwomanwith afive-year history ofmuscle cramps, right hand and distal lower limbweakness after longstanding efforts. She only startedwalking at the age of 30months but had no other motor development problem. Her father had a history of disabling demyelinating motor– sensory neuropathy. On neurological examination, she had bilateral pes cavus, slight weakness on right thumb abduction, bilateral foot dorsiflexion and hallux extension weakness (4/5); there was a generalized areflexia and distal lower limb light touch and pinprick hypostesia and few errors on postural sense testing; walking on heels was impaired. Motor conduction studies showed low velocities with prolonged latencies, with absent motor responses in feet. Partial conduction blocks were present in the median and ulnar nerves at the forearm (below elbow), more severe aftermuscular fatigue. Sensory potentialswere absent (lower limbs) or small. Laboratorial evaluation includingCSFanalysis was unremarkable. The genetic study was positive for the 233C > T mutation at the MPZ gene. Conclusion: This case illustrates the electrophysiological heterogeneity of CMT1B and adds this entity to conduction block differential diagnosis.