ACUTE DYSTONIA DEFINITION Dystonia is a brief or sustained muscle spasm, often with slow abnormal movements. Although any muscle group may be involved, it most commonly affects facial muscles (eyes, jaw, tongue). TOXIC CAUSES Numerous pharmaceutical agents are associated with acute dystonic reactions. Important examples include: Benzamides: metoclopramide sulpiride Butyrophenones: haloperidol Chloroquine and hydroxychloroquine Cocaine Levodopa Lithium Phenothiazines, especially piperazine compounds: trifluoperazine perphenazine fluphenazine prochlorperazine thiethylperazine Serotonin syndrome and neuroleptic malignant syndrome are specific toxic syndromes, associated with increased muscle tone, that require specific management. NON-TOXIC CAUSES Degenerative: Spinocerebellar degeneration Focal dystonias: Blepharospasm Writer's cramp Infective: Encephalitis Tetanus Metabolic: Thyrotoxicosis Wilson's disease Structural: Arterio-venous malformation Cerebrovascular accident Tumour CLINICAL FEATURES Onset of dystonia may occur up to 20 hours following the administration of the causative agent. Various types of dystonia, involving particular muscle groups have been described: Laryngeal dystonia - spasm of pharyngeal and laryngeal muscles resulting in stridor. Oculogyric crisis - spasm of extra-ocular muscles, forcing the eyes into upward or lateral gaze. Opisthotonus - spasm of all paravertebral muscles, forcing the trunk and neck into hyperextension. Retrocollis - spasm of paravertebral neck muscles, forcing the neck into hyperextension. Torticollis - spasm of lateral neck muscles, twisting the neck to one side. DIFFERENTIAL DIAGNOSIS Catatonic states Dyskinesias Seizures (tonic phase) RELEVANT INVESTIGATIONS Usually, no specific investigations are required to evaluate acute toxic dystonias. Where indicated, the following may be useful: CPK EEG or CT scan of head (to exclude seizures or central organic lesions) Toxicology screens Urinalysis TREATMENT Dystonias may increase in severity after initial presentation and therefore all patients should be treated. Initial treatment is usually provided with a parenteral formulation, followed by oral medication for 2 to 3 days to prevent recurrence. Milder forms can be treated with oral medication alone. Suggested agents include: Benztropine 1 to 2 mg by intramuscular or intravenous injection (0.02 mg/kg in children). This dose may be repeated in 10 minutes if the response is incomplete and anticholinergic side effects have not occurred. Follow with 1 mg (0.02 mg/kg in children) orally every 12 hours for 2 days. Benztropine is not the agent of choice in children less than 3 years of age. Diphenhydramine 1 mg/kg intravenously or intramuscularly to a maximum of 30 mg. This dose may be repeated in 30 minutes if the response is incomplete and anticholinergic side effects have not occurred. Follow with 25 mg (0.5 mg/kg in children) orally, every 6 hours for 2 days. Diazepam 0.1 mg/kg by slow intravenous injection. This dose may by repeated in 30 minutes if the response is incomplete and excessive sedation has not occurred. Procyclidine 5 to 10 mg (0.5 to 2 mg in children under 2 years of age, 2 to 5 mg in children over 2 years of age) intramuscularly or intravenously. This dose may be repeated after 20 minutes if the response is incomplete. Follow with 2.5 mg orally every 8 hours for 2 days. CLINICAL COURSE AND MONITORING Patients should be observed until symptom free. Prior to discharge, they should be instructed that recurrent dystonia can occur for up to 48 hours. In this event, they should return for medical evaluation. The clinical course may be prolonged in the case of dystonic reactions following injection of depot preparations. LONG-TERM COMPLICATIONS Unusual. AUTHOR(S)/PEER REVIEW Author: Robert Dowsett Consultant Toxicologist Departments of Clinical Pharmacology and Emergency Medicine Westmead Hospital Westmead, NSW 2145 Australia Peer Review: London, March 1998: P. Dargan, T. Della Puppa, L. Murray, A. Nantel, M. Nicholls.