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 s tretch-induced accessory nerve palsy obtained by using conventional te chnique compared to magnetic stimulation at the base of the skull. The same methods of magnetic stimulation were applied in 10 healthy volun teers, to determine normal limits of amplitude and latency of the moto r responses. The clinical features of the isolated spinal accessory ne rve palsy are weakness of the sternocleidomastoid muscle and of the th ree portions of trapezius muscle. Most commonly reported etiologies in clude surgical manipulation and excision in the posterior triangle of the neck. Less frequently the cause is represented by radiation proced ures, shoulder traction, penetrating, blunt or stretch injuries; this last etiology is extremely rare. The use of conventional electrophysio logical methods to evaluate injuries of the nerves leaving the base of the skull is limited by the difficulty in obtaining an adequate elect rical surface stimulation necessitating the use of needle electrodes. Moreover, conventional electrical stimulation often causes significant discomfort to the patient. The magnetic coil stimulation at the base of the skull is a new alternative painless technique that permits to e licit motor responses, by stimulating deeply situated nerves and, in p articular, the accessory nerve, resulting as a useful electrodiagnosti c tool.