[Age-related changes in nerve action potentials of median nerve--an analysis using intraneural neurography]

Age-related decrease in peripheral nerve conduction velocity and the amplitude of sensory nerve action potentials is well established in humans. However, evaluation of the sensory nerve action potentials is subject to technical constraints because of its small size and variability of the values. To elucidate age-related differences, we determined the amplitude of median nerve action potentials in 52 healthy individuals aged 16 to 88 years by means of intraneural neurography. A tungsten microelectrode was inserted into the median nerve trunk at the elbow, and compound nerve action potentials evoked by supramaximal electrical stimulation were recorded. The action potentials consisted mainly of triphasic waves. Maximal conduction velocity (Y, m/sec) declined very mildly with age (X, year), showing the regression line of Y = 67.5 - 0.062X. The peak to peak amplitude of the potentials was 466.6 +/- 20.8 (SE) microV and declined gradually with a decrement of 13 microV per decade in the individuals under the age of 50 years. By contrast, in individuals above the age of 50 years, the amplitude (Y, microV) declined steeply, showing the regression line of Y = 977.1 - 9.86X (r = -0.75, p < 0.001) with age (X, year). A significant correlation was observed between amplitude of the sensory nerve action potentials obtained by the conventional technique and that obtained by the intraneural neurography. Nevertheless, an accelerated decrease was not found in the amplitude of the sensory nerve action potentials with age above 50, probably due to the variability of the values.(ABSTRACT TRUNCATED AT 250 WORDS)