Nomogram for determining lower limit of the sural response

Objective Age and height influence on sural sensory nerve action potential (SNAP) have been studied separately. Our aim was to develop an equation for predicting the lower normal limits as a function of both these factors. Methods One hundred fifty-eight healthy volunteers, 63 male, with mean age 45.8 and mean height 167.3 without symptoms or signs of peripheral neuropathy participated in the study. The sural SNAP was recorded at the level of the ankle joint, just posterior to the lateral malleolus, using surface electrodes. Antidromic supramaximal stimulation was performed 13 cm proximally at the posterior midcalf. Results The mean sural SNAP amplitude was 19.9 ± 6.89 μV. Pearson linear correlation showed a negative correlation of the SNAP amplitude with age ( R = −0.22, p = 0.005) and height ( R = −0.19, p = 0.03). The multiple linear regression model was applied for both parameters of age and height with SNAP amplitude as the dependent parameter, producing the following equation: SNAP amplitude = 62.45 − 0.1447 × Age − 0.2147 × Height. Conclusions Using our normal data, the computed lower limits of the 95% prediction interval for the sural SNAP amplitude of an individual subject, depending on his age and height, were calculated. Significance The individualized normal values provided by our equation are essential for the correct interpretation of sural nerve studies.