A 60-year-old man presents with progressive tremor at rest in right hand, cogwheel rigidity, masked facies, and micrographia over 2 years. He fails a trial of levodopa. DaTscan is negative. Which alternative diagnosis should be strongly suspected?
- A Essential tremor
- B Multiple system atrophy (MSA)
- C Drug-induced parkinsonism ✓
- D Progressive supranuclear palsy (PSP)
Correct answer: C. Drug-induced parkinsonism
Explanation
A negative DaTscan (dopamine transporter imaging) indicates intact nigrostriatal dopaminergic neurons, ruling out idiopathic Parkinson's disease and other neurodegenerative parkinsonisms (MSA, PSP). The most common cause of parkinsonism with a negative DaTscan is drug-induced parkinsonism from dopamine-blocking agents (antipsychotics, metoclopramide, prochlorperazine). Medication history is critical. Essential tremor is predominantly postural/kinetic, not rest tremor. MSA and PSP have abnormal DaTscans.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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