Pathophysiology and treatment of cranial dystonia

Patients with cranial dystonia have blepharospasm,oromandibular dystonia, or a combination of both.Blepharospasm is characterised by involuntary spasms ofthe orbicularis oculi (OO) muscles, which result in forcefuleyelid closure. Oromandibular dystonia consists ofcontractions of the perioral or masticatory muscles, orboth, resulting in jaw-closing movements, lip or tongueprotrusion, and lower facial twitching.Electromyographic (EMG) studies indicate that involuntaryspasmodic contractions in blepharospasm canarise from various parts of the OO. The OO muscle consistsof three functional components: the pretarsal regionis mainly responsible for spontaneous, voluntary, or reflexblinking; the preseptal part for blinking and sustainedactivities (unilateral or bilateral narrowing or closureof the eyelids); and the orbital part is involved insustained contraction of the eyelids.In patients with blepharospasm, combining EMG recordingsfrom the OO and levator palpebrae (LP)muscles, Aramideh and colleagues1,2 identified three distinctpatterns of involuntary muscle activity, all showingthe typical features of EMG activity observed in otherforms of focal dystonia, namely, excessive muscle activityin the target muscle, co-contraction of antagonists,and failed voluntary activation of a target muscle. Thefirst EMG pattern is characterised by involuntary dischargesconfined to the OO with preservation of reciprocalinhibition in LP and OO muscles. The secondshows involuntary activity in the OO accompanied eitherby LP involuntary inhibition or disturbed OO-LP reciprocalinnervation. The third EMG pattern consists of LPinvoluntary inhibition alone, and when patients try toopen the eyes, the EMG shows involuntary LP inhibitionbut no OO activity