A 58-year-old man from Delhi is evaluated for progressive motor symptoms consistent with Parkinson disease. What is the most common cause of secondary parkinsonism in India?

Explanation

## Most Common Cause of Secondary Parkinsonism **Key Point:** Drug-induced parkinsonism is the most common cause of secondary parkinsonism globally and in India, accounting for up to 25–30% of all parkinsonism cases. ### Drugs That Cause Parkinsonism **High-Yield:** The mechanism is dopamine D~2~ receptor antagonism in the basal ganglia. | Drug Class | Examples | Mechanism | |------------|----------|----------| | Antipsychotics (typical) | Haloperidol, chlorpromazine | D~2~ antagonism | | Antipsychotics (atypical) | Risperidone, paliperidone | D~2~ antagonism (less than typical) | | Antiemetics | Metoclopramide, prochlorperazine | D~2~ antagonism | | Antidepressants | SSRIs (fluoxetine, sertraline) | Serotonergic effects | | Calcium channel blockers | Cinnarizine, flunarizine | D~2~ antagonism | | Lithium | — | Unclear; direct toxicity | | Valproate | — | Rare; mechanism unclear | **Clinical Pearl:** Drug-induced parkinsonism typically develops within weeks to months of drug initiation, is dose-dependent, and **reverses within weeks to months** of drug discontinuation — a key distinguishing feature from idiopathic PD. ### Why Other Options Are Less Common in India ```mermaid flowchart TD A[Secondary Parkinsonism in India]:::outcome --> B{Cause?}:::decision B -->|Drug-induced| C[Antipsychotics, antiemetics<br/>Most common 25-30%]:::action B -->|Vascular| D[Small vessel disease<br/>Less common 5-10%]:::action B -->|Post-infectious| E[Japanese encephalitis, others<br/>Rare in urban India]:::action B -->|Toxic| F[Manganese, carbon monoxide<br/>Occupational exposure rare]:::action ``` **Mnemonic:** **DIPS** = **D**rug-**I**nduced **P**arkinsonism is **S**upreme (most common secondary cause). ### Distinguishing Drug-Induced from Idiopathic PD | Feature | Drug-Induced | Idiopathic PD | |---------|--------------|---------------| | Onset | Acute/subacute (weeks–months) | Insidious (months–years) | | Tremor | Rare | Common (70%) | | Rigidity & bradykinesia | Prominent | Prominent | | Reversibility | Yes (after drug withdrawal) | No | | Response to levodopa | Poor | Excellent | **Warning:** Metoclopramide and prochlorperazine are commonly used in India for nausea and vertigo; clinicians must maintain high suspicion for drug-induced parkinsonism in patients on these agents.