Trigemino-facial inhibitory reflexes in idiopathic hemifacial spasm.

We investigated trigemino-facial excitatory and inhibitory responses in perioral muscles in hemifacial spasm (HFS). We examined 15 patients affected with idiopathic HFS and 8 healthy controls. Five patients had spasms mostly limited to the periocular region and 10 had spasms also involving the perioral muscles. Responses were recorded from the resting orbicularis oculi (OOc), levator labii superioris (LLS) and orbicularis oris (OOr) muscles, after supraorbital (SO) nerve stimulation and during isolated voluntary contraction of LLS muscle. Eight patients showed complete or partial preservation of the late silent period (SP2) in activated LLS muscle. The remaining 7 patients showed absence of SP2. Early and late excitatory responses were variably present in LLS muscle at rest. Patients with HFS clinically restricted to periocular muscles had at least partial preservation of the SP2. In conclusion, in HFS patients inhibitory trigemino-facial reflexes are impaired and excitatory trigemino-facial responses are elicited in perioral muscles. These two phenomena seem to develop independently; the degree of trigemino-facial reflex impairment parallels the extension of involuntary movements to the lower facial muscles.