A 30-year-old man with schizophrenia on haloperidol develops involuntary rhythmic movements of the tongue and lips with grimacing, three years into treatment. These movements persist even after haloperidol is stopped. What is this adverse effect, and what is the most likely mechanism?

• A Acute dystonia — sudden blockade of D2 receptors in the striatum
• B Drug-induced parkinsonism — depletion of dopamine in the nigrostriatal pathway
• C Tardive dyskinesia — supersensitivity of D2 receptors due to prolonged blockade ✓
• D Akathisia — blockade of D2 receptors in the mesolimbic system

Explanation

Tardive dyskinesia consists of late-onset, repetitive orofacial and choreiform movements developing after months to years of antipsychotic use, and may persist after stopping the drug. The mechanism involves chronic D2 receptor blockade causing receptor upregulation (supersensitivity) in the striatum, so that any dopamine stimulation becomes excessive. Acute dystonia occurs within hours to days of starting treatment. Drug-induced parkinsonism mimics PD but is reversible on drug withdrawal. Akathisia is subjective motor restlessness, not orofacial movements.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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