Acute Dystonic Reaction

An acute dystonic reaction is a movement disorder characterized by involuntary contractions of muscles that typically develops within minutes or hours following the administration of certain medications, particularly dopamine receptor antagonists like antipsychotics and antiemetics.  

Different muscle groups can be affected, and the reaction may be further categorized based on the specific muscles involved. For example, an oculogyric crisis involves the ocular muscles while laryngeal dystonia involves the larynx. Acute dystonic reactions are often abrupt, distressing, and can be potentially life-threatening, especially if they involve the oropharyngeal or respiratory muscles.

Acute dystonic reactions occur as a result of the effects of certain medications on the pathways of the brain that control voluntary movement. They are one of the most common extrapyramidal side effects, which are medication-induced movement disorders that range from dystonia to parkinsonism.  

Most commonly, acute dystonic reactions occur in response to antidopaminergic agents and dopamine receptor antagonists, such as antiemetics (e.g., metoclopramide) and antipsychotics (e.g., haloperidol, olanzapine, quetiapine, risperidone). Dopamine is a neurotransmitter that plays a key role in coordinating movement. In the basal ganglia, dopamine interacts with other neurotransmitters, like acetylcholine, to keep movements smooth and balanced. Normally, dopamine has an inhibitory effect on acetylcholine, meaning that when dopamine receptors are blocked, acetylcholine activity overrides dopamine activity. This imbalance causes overactivity in certain muscle groups, leading to involuntary muscle contractions that result in abnormal twisting movements or postures.  

While acute dystonic reactions can occur in people of all ages, they are more common in young individuals, particularly when exposed to high-potency antipsychotic medications like haloperidol. Using high doses of medication or a rapid dose escalation also increases the risk of dystonic reactions, as the body has less time to adapt to the dopamine blockade.  

Common signs and symptoms of an acute dystonic reaction are involuntarily contracted muscles in an atypical position, along with accompanying pain. Acute dystonic reactions often develop within minutes to days of initially starting a medication. The ocular muscles, jaw, tongue, face, neck, and trunk of the body are most often affected.  

An acute dystonic reaction may also cause characteristic postures, such as backwards tilting of the head, rotation of the head, or an eye looking in one direction. While acute dystonia is distressing, it is not usually life-threatening. The one exception is when there’s involvement of the laryngeal muscles, as this can cause airway compromise, resulting in stridor (i.e., a high-pitched breathing sound made by the collapsed airway), hoarseness, and labored breathing.  

An acute dystonic reaction is typically diagnosed through medical history, including current medications, and a physical examination. This exam often involves neuromuscular testing to examine the range of motion of the affected area, breathing ability, swallowing, and speech. Characteristically, individuals with acute dystonic reactions usually have a clear mental status. Altered consciousness might indicate other conditions such as neuroleptic malignant syndrome or serotonin syndrome. 

Finally, acute dystonia may mimic other conditions, including tetanus, seizures, and electrolyte abnormalities such as hypocalcemia and hypomagnesemia. While not necessary for the diagnosis, laboratory tests (e.g., electrolytes, renal function) may be checked to rule out metabolic causes of dystonia in unclear cases. 

An acute dystonic reaction is usually treated with anticholinergic agents (e.g., benztropine) or benzodiazepines (e.g., diazepam). Most often these medications are administered intravenously or intramuscularly since individuals may have difficulty swallowing. In cases of laryngeal dystonia, emergent care including supplemental oxygen and management of the airway may be necessary. It’s also typically advised to withdraw or reduce any medication that is responsible for the reaction. 

 For individuals with a prior history of acute dystonic reactions, preventive strategies include using the lowest effective doses of antipsychotics or antiemetics, opting for medications with lower dystonic potential, and gradual titration when initiating therapy. Prophylactic use of anticholinergic agents may also be considered in high-risk individuals.