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Introduction
Movement disorders can occur as a side effect of many different pharmacological agents, including antidepressants, antiepileptics, and cholinesterase inhibitors. Most commonly, these “extrapyramidal” side effects occur after exposure to dopamine receptor blocking drugs, including antipsychotics, antiemetics, and gastrointestinal promotility agents. Extrapyramidal side effects can be broadly divided into four categories: parkinsonism, akathisia, acute dystonic reactions, and tardive dyskinesia. While drug-induced parkinsonism and akathisia commonly occur after weeks to months of treatment with antipsychotics, and tardive dyskinesia after months to years, acute dystonic reactions to medications usually present within the first few days of treatment, often after a single dose [42]. In this chapter, we discuss the phenomenology and prevalence of acute dystonic reactions, their association with various medications and their possible underlying pathophysiology.
Phenomenology
Acute dystonia is the earliest drug-induced movement disorder syndrome to appear and may arise after taking just a single dose of medication. Almost all drug reactions that fit within this category arise within the first 5 days of treatment [6], [65]. The fairly rapid disappearance of acute dystonic reactions on withdrawal of the offending drug is also one of its essential clinical features [20].
Acute dystonic reactions are characterized by abrupt onset of involuntary movements that most commonly involve the face and neck, but can also or only involve the trunk and extremities. Involvement of the face manifests as oculogyric crises, blepharospasm, trismus, forced jaw-opening, grimacing, protrusion, or twisting of the tongue and distortions of the lips. Neck and throat involvement includes laryngeal or pharyngeal dystonia, torticollis, or retrocollis. Dysarthria, dysphagia, jaw dislocation, and respiratory stridor may result [42]. In severe cases, acute laryngeal dystonia can lead to life-threatening respiratory distress following partial or complete obstruction of the upper airway [12]. Involvement of the trunk may give rise to scoliosis, lordosis, opisthotonos, tortipelvis, and a characteristic dystonic gait [42]. The acute dystonia and dyskinesias are distressing, frightening, and may be painful.
Individual susceptibility
Acute dystonic reactions occur in only a proportion of people exposed to relevant medications. Some factors contributing to increased susceptibility to acute dystonic reactions have been delineated. Younger patients seem to be more susceptible to develop acute dystonic reactions, while older patients are more likely to develop drug-induced parkinsonism [6], [65]. The latter can be explained by differences in proposed pathophysiology between the two conditions (see below). The incidence of acute dystonia was twice as high in men as in women in one study [6]. Clinical features of dystonia also seem to differ per age category, with younger patients showing more severe and generalized involvement of the trunk and extremities, while older individuals tend to show more restricted involvement of the neck, face, tongue, and upper extremities [42], [6]. It is difficult to know if some of these differences (particularly the gender differences) have to do with the use of higher doses of antipsychotic medications in men versus women with acute psychosis.
Drugs inducing acute dystonia
Dopamine receptor blocking agents
Dopamine receptor blocking drugs (DRBs) are used primarily as antipsychotic medications, but are also used as antiemetics and gastrointestinal promotility agents. This class of drug is the one most often associated with acute dystonic reactions. Acute dystonic reactions occur in about 1%–3% of patients receiving antipsychotic medication [6], [61], [5]. Whereas acute dystonia tends to occur more frequently with use of highly potent DRBs like haloperidol [65], newer atypical antipsychotics such as aripiprazole and olanzapine can also induce these side effects (see Tables 2.1 and 2.2). The frequency of acute dystonic reactions in patients using haloperidol was as high as 16% in the study by Swett [65], while others have reported an incidence of 7.3%, 2.3%, and 2% [64], [61], [5].
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