Acute Dystonic Reaction

An acute dystonic reaction is a sudden extrapyramidal adverse effect caused by a dopamine-receptor-blocking drug. Blockade of dopamine D2 receptors in the nigrostriatal pathway leaves cholinergic activity relatively unopposed in the basal ganglia. Motor pathways then become excessively activated, producing sustained, often painful muscle contractions rather than a brief twitch or tremor. The timing is one of the strongest clues. About half of reactions occur within 48 hours of starting the drug or increasing its dose, and approximately 90% occur within 5 days. A patient who develops a fixed neck position, jaw spasm, or forced upward eye deviation soon after receiving a dopamine antagonist has a recognizable medication-related pattern until proven otherwise. Dose matters. Higher doses and greater striatal D2-receptor occupancy increase the risk of extrapyramidal symptoms. High-potency first-generation antipsychotics, particularly haloperidol, are frequent causes, but acute dystonia can also follow exposure to second-generation antipsychotics and dopamine-blocking antiemetics.