Intraoperative compound muscle action potentials (CMAPs) amplitude changes after decompression and neurolysis of peripheral nerves in upper limbs neuropathies: Electrophysiologial considerations and relation with clinical outcome

BACKGROUND: Decompression and, when necessary, neurolysis in entrapment neuropathies of upper limbs are effective and safe procedures, but their correlation with the variation of compound muscle action potentials (CMAPs) is still unclear, based in particular on experimental models. In addition, there are few data regarding the efficacy of intraoperative neurophysiologic monitoring (IOM) to predict clinical early and late outcome after surgery in term of pain control and sensitive/motor recovery. We report about the association between the intraoperative anatomical and neurophysiological findings and the mid- and long-term postoperative clinical course in a surgical series. METHODS: We retrospectively reviewed clinical data of 24 patients among 68 admitted at our Institution for upper limb neuropathies from September 2012 to May 2015. All patients completed two preoperative questionnaires for assessing the level of disability (DASH) and of pain/ discomfort (NRS). CMAPs' amplitudes were intraoperatively detected, before and after decompression and neurolysis and the variations were then related to clinical outcome, evaluated through DASH and NRSquestionnaires at 6-, 9- and 12-months follow-up. RESULTS: A statistically significant difference was noted in CMAPs amplitudes before and after decompression (P<0.01). In two patients, this variation was so satisficing to determinate the end of procedure, without the need to perform neurolysis. Major correlations between the variation of CMAPs amplitude after surgery and change of DASH and NRSscores at follow-up were found. CONCLUSIONS: Variations of CMAPs amplitude provide real-time information on nerves function and may be helpful in predicting mid- and long-term postoperative outcome regarding pain relief and neurological functions.