Selection of electrophysiological techniques to investigate axonal damage of peripheral motor nerve fibres.

After an acute peripheral nerve injury fibrillations and positive sharp waves can be registered in the denervated muscle. The time delay between injury and the manifestation of detectable electrophysiological alterations using conventional electromyography (EMG) lessens the diagnostic value for early treatment. We demonstrate that in radicular lesions the electromyographic examination of the paravertebral musculus multifidus allows diagnosis earlier by about a week compared to examination of limb muscles. Using the amplitude reduction of the compound muscle action potential (CMAP) after stimulation of the nerve distal to its lesion a further reduction of the delay for electrophysiologic proof in peripheral as well as in radicular lesions is possible. Based on these findings we propose a selective strategy using the decline of the CMAP starting with the third day after a peripheral nerve lesion, the electromyography of the deep paravertebral muscles in radicular lesions beginning at the end of the first week, and the conventional EMG investigation of limb muscles after two weeks following the injury.