Magnetic stimulation of the spinal accessory nerve: normative data and clinical utility in an isolated stretch-induced palsy.

We report the clinical and electrophysiological findings of isolated stretch-induced accessory nerve palsy obtained by using conventional technique compared to magnetic stimulation at the base of the skull. The same methods of magnetic stimulation were applied in 10 healthy volunteers, to determine normal limits of amplitude and latency of the motor responses. The clinical features of the isolated spinal accessory nerve palsy are weakness of the sternocleidomastoid muscle and of the three portions of trapezius muscle. Most commonly reported etiologies include surgical manipulation and excision in the posterior triangle of the neck. Less frequently the cause is represented by radiation procedures, shoulder traction, penetrating, blunt or stretch injuries; this last etiology is extremely rare. The use of conventional electrophysiological methods to evaluate injuries of the nerves leaving the base of the skull is limited by the difficulty in obtaining an adequate electrical surface stimulation necessitating the use of needle electrodes. Moreover, conventional electrical stimulation often causes significant discomfort to the patient. The magnetic coli stimulation at the base of the skull is a new alternative painless technique that permits to elicit motor responses, by stimulating deeply situated nerves and, in particular, the accessory nerve, resulting as a useful electrodiagnostic tool.