A 45-year-old man with a 15-year history of schizophrenia on haloperidol 10 mg/day develops repetitive, involuntary chewing movements and tongue protrusions that persist for 6 months. He scores 4 on the AIMS. Which mechanism best explains this adverse effect?

• A Cholinergic excess in the basal ganglia
• B Dopamine D2 receptor upregulation and supersensitivity in the nigrostriatal pathway ✓
• C Serotonergic depletion in the mesolimbic pathway
• D GABA-ergic inhibition of the subthalamic nucleus

Explanation

Tardive dyskinesia (TD) arises from prolonged D2 receptor blockade leading to upregulation and supersensitivity of postsynaptic D2 receptors in the striatum (nigrostriatal pathway). When dopamine activity fluctuates or the drug is reduced, these supersensitive receptors mediate hyperkinetic involuntary movements. The AIMS (Abnormal Involuntary Movement Scale) is used to monitor TD severity. Cholinergic excess is associated with drug-induced parkinsonism, not TD.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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