Anterior shin muscles CMAP measurements: Normal limits of symmetry and intra- and interobserver reliability

OBJECTIVE: The normal limits of symmetry for the compound muscle action potential of the shin muscles (CMAPshin) have not been determined yet. The goal of this study is to provide extensive data on the limits of symmetry and the reliability of CMAPshin. METHODS: The study was conducted in normal healthy males and females. All subjects underwent CMAPshin measurements bilaterally. The median percent differences of right/left amplitude/area, with range of these measurements, were calculated. In addition, the intra- and interobserver reliability was examined in a separate population. RESULTS: The study group consisted of 58 healthy individuals. The median percent right/left difference for amplitude and area were respectively 7.2% (range 0–23.6%) and 5.4% (range 0.7–25.6%). Right/left difference of the amplitude/area of the CMAPshin greater than 24%/26% respectively can be considered as pathological. The Pearson correlation coefficients (r) for the intra-observer reliability amplitude/area are 0.905/0.882 and for the inter-observer reliability are 0.968/0.981. CONCLUSIONS: The results confirm symmetry and good intra- and interobserver reliability in CMAPshin measurements. SIGNIFICANCE: CMAPshin can be used in practice to estimate axonal loss in case of a foot drop. Data studies examining symmetry of CMAPshin can facilitate in the clinical interpretation of these nerve conduction studies.