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 of the orbicularis oculi (OO) muscles, which result in forceful eyelid closure. Oromandibular dystonia consists of contractions of the perioral or masticatory muscles, or both, resulting in jaw-closing movements, lip or tongue protrusion, and lower facial twitching. Electromyographic (EMG) studies indicate that involuntary spasmodic contractions in blepharospasm can arise from various parts of the OO. The OO muscle consists of three functional components: the pretarsal region is mainly responsible for spontaneous, voluntary, or reflex blinking; the preseptal part for blinking and sustained activities (unilateral or bilateral narrowing or closure of the eyelids); and the orbital part is involved in sustained contraction of the eyelids. In patients with blepharospasm, combining EMG recordings from the OO and levator palpebrae (LP) muscles, Aramideh and colleagues 1,2 identified three distinct patterns of involuntary muscle activity, all showing the typical features of EMG activity observed in other forms of focal dystonia, namely, excessive muscle activity in the target muscle, co-contraction of antagonists, and failed voluntary activation of a target muscle. The first EMG pattern is characterised by involuntary discharges confined to the OO with preservation of reciprocal inhibition in LP and OO muscles. The second shows involuntary activity in the OO accompanied either by LP involuntary inhibition or disturbed OO-LP reciprocal innervation. The third EMG pattern consists of LP involuntary inhibition alone, and when patients try to open the eyes, the EMG shows involuntary LP inhibition but no OO activity. Brainstem Reflexes