Dystonia

Dystonia is a movement disorder of sustained or intermittent muscle contractions causing abnormal twisting postures and repetitive movements.

• Classification: age of onset, body distribution (focal, segmental, multifocal, generalised), temporal pattern, associated features; acquired versus inherited versus idiopathic.

• Genetic forms: DYT1 (TOR1A, early onset generalised), DYT-GCH1 (dopa responsive), THAP1, others. Acquired: stroke, perinatal injury, drugs (neuroleptics, metoclopramide), Wilson disease.

• Network disorder of basal ganglia, cerebellum and sensorimotor cortex.

• Task specific dystonia (writer cramp), blepharospasm, oromandibular, cervical, laryngeal, limb dystonia, generalised.

• Sensory trick (geste antagoniste) transiently relieves; overflow phenomena; worsens with stress and fatigue.

• Dystonic tremor; pain.

• Acute dystonic reaction after neuroleptics, oculogyric crisis.

• Clinical diagnosis by pattern.

• Early onset (under 30) or generalised: trial of levodopa to exclude dopa responsive dystonia; copper, caeruloplasmin, slit lamp for Wilson disease; MRI brain (basal ganglia, NBIA); genetic panel (TOR1A, GCH1, THAP1, ATP1A3, others).

• Review medications; consider tardive dystonia.

• Exclude functional dystonia (inconsistency, distractibility).

• Focal dystonia: botulinum toxin type A injections every 3 months (onabotulinumtoxinA, abobotulinumtoxinA, incobotulinumtoxinA) are first line.

• Oral medication: trihexyphenidyl 2 mg increasing to 6 to 30 mg daily in divided doses (anticholinergic effects), baclofen 5 to 20 mg three times daily, clonazepam 0.5 to 2 mg, tetrabenazine 12.5 to 75 mg (tardive dystonia).

• Levodopa/carbidopa 100/25 mg: trial 1 to 3 months for dopa responsive dystonia.

• Acute dystonic reaction: procyclidine 5 to 10 mg IM/IV or benztropine 1 to 2 mg IV, stop the offending drug.

• Generalised or refractory dystonia: deep brain stimulation of the globus pallidus internus (clinical improvement 50 to 60%).

• Physiotherapy, sensory trick training, psychological support.

• Genetic counselling.