MAGNETIC TRANSCRANIAL AND ELECTRICAL STYLOMASTOIDAL STIMULATION OF THE FACIAL MOTOR PATHWAYS IN BELLS-PALSY - TIME-COURSE AND RELEVANCE OF ELECTROPHYSIOLOGICAL PARAMETERS

Facial nerve motor neurography was performed at various times after th e onset of Bell's palsy in 97 patients. Stimulation of the facial nerv e was performed (1) electrically in the fossa stylomastoidea (ElStim), and (2) magnetically in the labyrinthine segment of the facial canal (MagStim), evaluating different coil positions over the skull. Additio nally, the face-associated motor cortex was stimulated magnetically in 47 patients (CxStim). A marked reduction of the amplitudes of the com pound muscle action potentials (CMAP) evoked by MagStim on either m. n asalis or mentalis, or both, was observed which was clearly more prono unced than the amplitude reduction to ElStim. This discrepancy occurre d very early during the disease, the mean amplitude (expressed in perc ent of the amplitude on the unaffected side) being 82% (S.D. 9.1) for ElStim and 1% (2.7) for MagStim at days 0-4. It persisted for several months, often when facial nerve function had recovered to normal, as a ssessed by clinical observation, ElStim, and CxStim. This amplitude de crease to MagStim, which appears to be related to a locally enhanced s timulation threshold of the facial nerve, is a very sensitive and repr oducible finding in Bell's palsy. It may prove specific of the disorde r, of diagnostic value, and of interest in the follow-up of patients d uring treatment trials.