Anterior interosseous nerve syndrome.

Details of a 23 year old patient who suffered the spontaneous onset of an anterior interosseous nerve palsy are recorded together with the results of a full neurophysiological investigation. Isolated lesions of the anterior interosseous nerve are rare and there are no recorded cases with comprehensive neurophysiological investigation. The anterior interosseous nerve is a purely motor nerve and supplies the flexor pollicis longus, flexor digitorum profundus to the index and middle fingers and pronator quadratus muscles. The detailed anatomy and its normal variation has been discussed by A 23 year old male labourer found difficulty in picking up a cup of tea on a Sunday morning in July 1971; this was apparently due to weakness of the right thumb and index finger. He had no pain or paraesthesiae at any time. It may be relevant that he had drunk about 10 pints of beer the night before and slept well. He was first seen two months later and there had been no real change in his symptoms. Examination showed no voluntary flexion of the terminal phalanx of the right thumb, and flexion of the terminal phalanx of the right index finger was very weak (MRC Grade 1) when the proximal interphalangeal and the metacarpophalangeal joints were fully extended. There was also weakness of flexion of the terminal phalanx of the middle finger (MRC Grade 3). Pronator quadratus is a difficult muscle to test in isolation, but there was undoubted weakness of pronation of the right forearm when the elbow was fully flexed to minimize the effect of the pronator teres muscle. There was no weakness of abductor pollicis brevis, flexor digitorum sublimis, or any of the small hand muscles and there was no sensory deficit. 531 NEUROPHYSIOLOGICAL INVESTIGATION The patient lay supine and relaxed on a couch. An infra-red lamp was used to maintain the surface temperature of both arms at 370 C. Stimulation andrecording Motor conduction studies and antidromic sensory action potentials were recorded from both median nerves after stimulation by cloth-covered silver electrodes, soaked in saline, placed 2-5 cm apart and applied over the nerve at the wrist or the elbow. The cathode was placed at the point of lowest threshold for M waves and 50 usec rectangular electrical pulses were delivered by a Devices stimulator type 3072 at a voltage which was supramaximal for M waves by 50 V. The same electrodes and placements were used for …