Conduction studies along the accessory nerve and follow-up of patients with trapezius palsy.

The accessory nerve was stimulated at the posterior triangle of the neck and responses were evoked simultaneously from the upper, middle and lower part of the trapezius muscle. Sixteen patients were investigated, 10 with trapezius palsy following surgical procedures at the posterior cervical triangle, three with a history suggestive of neuralgic amyotrophy and three of unknown origin. On the unaffected side the latency increases 0.16 ms per 10 mm increase in conduction distance corresponding to a conduction velocity of 63 m/s. Evidence is presented that the upper, middle and lower part of the trapezius muscle receive innervation from the accessory nerve. Follow-up of patients showed spontaneous nerve regeneration after complete axonal degeneration. These findings suggest that surgical intervention should be delayed to allow for spontaneous reinnervation. Clinical recovery was incomplete in cases of iatrogenic origin.