[Electrophysiological assessment of median sensory nerve function in HMSN type I by intraneural neurography]

Microneurography (MNG) performed in the forearm segment of the median nerve enabled us to assess compound nerve action potentials reflecting the density of large myelinated sensory fibers around the microelectrode. We examined sensory nerve function of the median nerve in seven patients with hereditary motor and sensory neuropathy type I (HMSN-I) with conventional surface-electrode technique and MNG. In six of seven patients sensory nerve action potentials were not elicited with the surface-electrode method. In contrast, compound nerve action potentials (CNAPs) were evoked in all seven patients with MNG. Although the normal waveform of CNAP is characterized by a large triphasic wave with subsequent small multiphasic waves, the triphasic wave was diminished and prolonged small multiphasic waves were prominent in the patients. Maximal nerve conduction velocity and amplitude of the wave were decreased to 69% and 9% of age-matched control values, respectively. These changes detected in patients with HMSN-I could be interpreted as a result of large myelinated fiber loss and segmental demyelination of sensory nerves. We showed that sensory fiber dysfunction in HMSN-I could be quantitatively evaluated with MNG, even though the sensory action potential was not elicited with the surface-electrode method.