A dystonic reaction is a sudden, involuntary muscle contraction that can be painful and startling. These reactions cause twisting movements and abnormal postures, often affecting the face, neck, and torso. They represent a type of adverse drug reaction, meaning they are an unwanted side effect of certain medications. This article aims to inform readers about common medications implicated in these reactions and outline appropriate responses if one occurs.
What is a Dystonic Reaction?
Dystonic reactions involve sustained or intermittent involuntary muscle contractions, leading to repetitive twisting movements or abnormal body postures. These spasms can affect various body parts, including the extremities, face, neck, abdomen, pelvis, or larynx. Common manifestations include upward eye deviation (oculogyric crisis), jaw clenching (trismus), tongue protrusion, or abnormal head and neck positions (torticollis).
While often frightening, dystonic reactions are not life-threatening, though laryngeal dystonia can, in rare cases, lead to airway obstruction. The underlying mechanism involves an imbalance of neurotransmitters, specifically dopamine and acetylcholine, within the basal ganglia of the brain. Medications that block dopamine receptors can disrupt this balance, leading to the uncontrolled muscle activity observed in these reactions. Reactions occur shortly after starting a new medication or increasing its dose.
Medications Known to Cause Dystonic Reactions
Many medications can cause dystonic reactions, primarily those that interfere with dopamine signaling in the brain.
Antipsychotics
Antipsychotic medications, also known as neuroleptics, are a common cause of drug-induced dystonia because they block dopamine D2 receptors. First-generation (typical) antipsychotics, such as haloperidol and chlorpromazine, carry a higher risk of inducing these reactions. The incidence of acute dystonic reactions in patients taking antipsychotics can range from about 1% to 3%, with higher rates, sometimes up to 16%, reported for high-potency agents like haloperidol.
Second-generation (atypical) antipsychotics, while still carrying a risk, are less likely to cause dystonic reactions. This reduced risk is attributed to their ability to balance dopamine blockade with muscarinic M1 receptor blockade. However, all currently known antipsychotic medications have some potential to cause an acute dystonic reaction.
Antiemetics
Antiemetic medications, used to prevent nausea and vomiting, are another frequent cause of dystonic reactions, particularly those that block dopamine receptors. Common examples include metoclopramide and prochlorperazine. The risk with metoclopramide has been reported to be around 0.5% in patients taking it for the first time, with a higher incidence of 1.2% in younger patients.
Promethazine, another antiemetic, has also been implicated.
Other Medications
Beyond antipsychotics and antiemetics, other drug classes can also contribute to dystonic reactions. Certain antidepressants, particularly selective serotonin reuptake inhibitors (SSRIs), can cause these reactions. Other less common culprits include some antimalarials, antihistamines, and anticonvulsants. Illicit drugs like alcohol and cocaine can also increase the risk of these reactions.
Responding to a Dystonic Reaction
If someone experiences a dystonic reaction, immediate medical attention should be sought. Call emergency services or go to the nearest emergency room. Medical professionals can administer specific medications to quickly reverse the reaction.
Medical intervention involves anticholinergic agents, such as benztropine or diphenhydramine. Symptoms improve within 10 to 30 minutes following intravenous or intramuscular administration of these drugs. When seeking medical help, providing a complete list of all medications the person is currently taking is important, as this information guides the medical staff in their treatment.
Preventing Recurrence and Long-Term Management
Preventing future dystonic reactions involves careful medication management and patient education. After an acute reaction, medical professionals may continue oral anticholinergic medication for one to seven days to prevent symptoms from returning.
Reviewing all current medications with a doctor is important. Doctors may consider adjusting the dosage of the offending medication or switching to an alternative drug with a lower risk of causing dystonia. Patients should inform all healthcare providers about their history of dystonic reactions to ensure appropriate medication choices and monitoring.