[Superiority of intrafascicular neurography over conventional nerve conduction studies in evaluating axonal degeneration]

Abstract

We investigated conventional motor and sensory nerve conduction studies (MCS & SCS) with regard to the sensitivity in detecting axonopathies. Twelve patients with axonal type of polyneuropathy, 2 vincristin neuropathy and 10 cisplatin neuropathy, were examined by MCS & SCS. Their data were compared with those by intrafascicular microneurography (MNG) of the median nerve. Nerve conduction velocities were within normal limits or slightly reduced to 87-99% of the normal. Amplitude of compound muscle action potential (CMAP) by MCS decreased to 4 or 5 mV in vincristin neuropathy, though cisplatin neuropathy presented normal amplitude. Amplitude of sensory nerve action potential (SNAP) by SCS was undetected in one median nerve and in three sural nerves. While, compound nerve action potential (CNAP) by MNG was all recorded, and presented the amplitude value of below 150 microV in seven patients. The waveform was normal or mild neuropathic pattern. No patients presented normal CNAP amplitude and reduced SNAP amplitude. But there were three patients who had normal SNAP amplitude and reduced CNAP amplitude. In SCS we could recognize abnormal only after CNAP amplitude by MNG dropped to below 100 microV. Cisplatin neuropathy demonstrates reduction of CNAP or SNAP amplitude, and vincristin neuropathy further presents reduction of CMAP amplitude. Evaluation of axonopathy is best achieved by nerve action potential amplitude. Conventional surface electrode methods are available for this purpose, but MNG is more sensitive and is capable of quantitative analysis even in severely damaged nerves.