Selective anterior interosseous nerve conduction study: Coaxial needle versus surface electrode recordings.

OBJECTIVES

The aim is to determine which method provides the most selective motor nerve conduction of the anterior interosseous nerve (AIN), when the stimulation cannot be restricted to this nerve.

METHODS

The AIN was stimulated at the elbow, along with the whole median nerve. The motor action potential (MAP) of the AIN was recorded with 2 different methods: 1 - a coaxial needle inserted in the pronator quadratus muscle (PQ); 2 - a pair of surface electrodes fixed on the PQ. Twenty-two controls and 4 patients with AIN palsy were studied with both methods. Two among the patients were also examined with a 3rd method involving a pair of surface electrodes fixed on the flexor pollicis longus.

RESULTS

For controls, with needle recording, distal motor latency (DML) to the PQ was 4.2ms and PQ MAP amplitude was 15.0mV. With surface recording, distal motor latency (DML) to the PQ was 3.1ms and PQ compound MAP (CMAP) amplitude was 5.1mV. For patients, with needle recording, DML was normal, and MAP amplitude was drastically decreased as compared with controls, while with surface recording, DML and CMAP amplitude showed no substantial change.

DISCUSSION AND CONCLUSIONS

These results demonstrate that recording with a coaxial needle electrode inserted in the PQ is the only method to provide a specific NCS of the AIN, and permit the diagnosis of isolated AIN lesions, which could otherwise be missed.