The quantification of motor units in carpal tunnel syndrome by motor unit estimation

The "motor unit estimation" (MUE) is one refined and noninvasive method to determine the approximate number of motor units within a certain muscle. Th e study comprises the estimation of excitable motor units in the median ner ve innervated thenar muscles in 25 patients with carpal tunnel syndrome (CT S) and 25 age matched normal controls. Multiple point stimulation of the me dian nerve was used to collect 10 of the lowest threshold, all-or-nothing m otor unit action potentials (s-MUAP). Median amplitude and area of s-MUAP w ere used to determine the motor unit estimate (MUE) by dividing the corresp onding value of the maximal compound muscle action potential. In almost all patients MUE were significantly lower than in normal controls. Amplitude b ased estimation of motor units was the most reliable parameter to distingui sh patients from normal controls. 12 patients were investigated by MUE thre e month after surgical therapy of CTS. The observation of increased numbers of excitable motor units in 7 of these patients, all with short history of complaints, indicates a previous partial conduction block of the median ne rve.