Occurrence of A‐waves in F‐wave studies of healthy nerves

A‐waves are compound muscle action potentials that follow the M‐wave with a constant shape and latency; usually they are detected during F‐wave studies. A large reference value database for F‐wave parameters from the median, ulnar, peroneal, and tibial nerves was collected from 121–196 subjects aged 14 to 95 years without known pathology involving the studied nerves. From this material, we studied retrospectively the occurrence of A‐waves. To be included, an A‐wave had to be clearly discriminated from the baseline in at least 8 of 20 traces with a jitter of less than 0.5 ms. A‐waves occurred in 25% of the tibial nerves studied and 14% of the peroneal nerves but in only 2% of median and ulnar nerves. In the peroneal and tibial nerves, the frequency of A‐waves increased with age, suggesting that A‐waves may be related to normal age‐related mild neuropathic changes of alpha motor neurons. Thus, A‐waves are frequently found in lower‐extremity nerves in healthy subjects and less commonly in upper‐extremity nerves. Their presence must therefore be interpreted with caution and cannot be taken as necessarily indicative of abnormality. Muscle Nerve 28: 626–629, 2003