Electrodiagnostic examination of the anterior interosseus nerve. Normal and pathologic data (21 cases).

The study reports the normal electrodiagnostic findings of anterior interosseus nerve (AIN) examination in 30 controls and the pathological features in 21 patients with AIN lesion. The main electrodiagnostic study considered pronator quadratus (PQ) needle examination and AIN conduction study to PQ. In controls PQ latency was 4.1 +/- 0.56 ms and the compound muscle action potential (CMAP) amplitude was 14.7 +/- 4.3 mV. In patients PQ latency was altered in 8 cases when CMAP amplitude, spontaneous activity and recruitment pattern were abnormal in 18 cases. In the 3 remaining cases diagnosis was assessed with the flexor pollicis longus (FPL) and/or the flexor digitorum profondus of the second digit (FDP2) needle examination. Out of 21 cases 12 presented with complete AIN lesion and 9 with incomplete AIN lesion. The recovery occurred 10/11 times spontaneously and mean recovery delay was 14.3 months. Five cases were related to compression and 16 cases to inflammatory lesion. When no traumatism is obvious, no surgery should be considered for the first 12 to 16 months as late spontaneous recovery can occur.