Hemifacial spasm or somatoform disorder - postexcitatory inhibition after transcranial magnetic cortical stimulation as a diagnostic tool

Hemifacial spasm (HFS) presents a frequent movement disorder. It is thought to have an organic origin. It therefore has to be distinguished from other facial involuntary movements, especially psychogenic ties, because the the rapeutic approach differs. The present study opted to evaluate the diagnost ic value of the postexcitatory inhibition (pI) after transcranial magnetic stimulation (TMS). After stimulating the contralateral hemisphere with the conventional flat coil and recording from the mentalis muscle, in 10 health y controls and 10 patients postexcitatory inhibition was determined. PI sho wed no side to side difference in healthy controls (96.9 +/- 12.7 ms right, 87.9 +/- 10.8 ms left side, interhemispheric difference 6.4 +/- 3.8 ms). I n 8 patients with hemifacial spasm, the duration of pI on the non-affected side did not differ from the healthy controls (87.9 +/- 43.5 ms). During sp asm, pi on the affected side shortened increasingly until no inhibition cou ld be induced. Afterwards the spasm pi was prolonged significantly (up to 1 40 ms longer than opposite side) before returning to normal values. Two pat ients presented no side differences of pi during the "spasm". An emotional conflict situation could be evaluated, supporting the diagnosis of somatofo rm disorder. As postexcitatory inhibition is mainly due to cerebral mechani sms, the electrophysiological results of the study pointed to a cortical in fluence on the hemifacial spasm. TMS seems to be an electrophysiological to ol which allows a differentiation between organic and psychogenic spasm and enables a different therapeutic approach.