Abstracts of the 8th Meeting of the Italian Peripheral Nerve Study Group: 49

Abstract

A 65‐year‐old woman was referred because of bilateral foot drop, pes cavus and distal muscular atrophy. Electrophysiological studies showed prolonged distal motor latencies and conduction velocities ranging from 33 to 42 m/s in upper limb nerves. A conduction block (P/D area = 0.4) was present in the wrist elbow segment of median nerve. Her 42‐year‐old daughter was asymptomatic and neurological examination revealed only absent deep tendon reflex. The 35‐year‐old son complained of positional paresthesias and had normal examination. The 13‐year‐old nephew was completely normal. There was no history of pressure palsies. All three proband's relatives showed: 1) normal or slightly slowed motor conduction velocities; 2) slowing of conductions in the above‐below elbow segment of both ulnar nerves (difference of velocity with the below elbow‐wrist segment ranging from 16 to 25 m/s). Sural nerve biopsy in the proband showed at light microscopy a chronic demyelinating and remyelinating process. On teased‐fiber examination virtually all fibers showed myelin thickenings or classical tomacula. Molecular analysis showed neither deletion of the 17p11.2 segment nor mutation of the PMP 22 gene. The sequence of MPZ/PO revealed a 306delA at codon 102 in the proband and three relatives. The mutation was of non‐sense type and causes a frameshift with a premature stop codon (Val102fs). Motor conduction velocities in CMT1B are usually < 20 m/s although a predominantly axonal variant with intermediate range conduction velocities has been also reported. Focally folded myelin has been reported in a few CMT1B patients usually, as in our cases, harboring a mutation in the extracellular domain of P0. In conclusion this CMT1B family is electrophysiologically peculiar because of the coexistence of intermediate‐normal motor conduction velocities with segmental slowing and conduction block. Focal conduction abnormalities may be pathophysiologically related to tomacula at the paranodal region.