Shingo Nobuta, Katsumi Sato and Eiji Itoi
Objective: Anterior interosseous nerve (AIN) lesions are rare and a few nerve conduction measurements have been reported. The purpose of this retrospective study was to assess the diagnostic value of the motor nerve conduction measurements for the AIN lesion and to investigate its electrodiagnostic features. Methods: Twenty-three patients with AIN lesion were reviewed after a mean follow-up of 13 months. Of these 23 cases, a complete palsy of flexor pollicis longus (FPL) and flexor digitorum profundus to the index finger (FDP1) was seen in five, and an isolated palsy of FPL in three and that of FDP1 in two, while pronator quadratus (PQ) was weak in twelve. The compound muscle action potential (CMAP) from the PQ muscle and the FPL muscle were recorded and analyzed. Twenty-two patients were treated conservatively and one underwent surgery. Results: Both PQ-CMAP and FPL-CMAP were recorded in all of the patients initially, and they all showed abnormality in PQ- and/or FPL-CMAP. Delayed latency and / or low amplitude were seen in 21 for PQ-CMAP and in 17 for FPL-CMAP. At the time of final follow-up, an improvement in the muscle strength of FPL, FDP1 and PQ was seen in 11 with the British Medical Research Council (MRC) grade 4 or better (complete recovery), whereas, partial recovery in 11 and unchanged in one. The decrease of amplitude in PQ-CMAP showed a significant difference between the normal PQ strength group and the weak PQ strength group. Conclusion: Recording and analysis of PQ- and FPL-CMAP are simple and safe and are important for the definite electrodiagnosis of AIN lesions. The data suggest that an axonal degeneration is main pathology.