Correct Answer: D. Selegiline
The clinical presentation—rigidity, tremors, and blank facial expressions (masked facies)—is pathognomonic for Parkinson's disease (PD). The cardinal motor features are the triad of resting tremor, rigidity, and bradykinesia; the blank facies reflects loss of spontaneous facial movement. Selegiline is a selective monoamine oxidase-B (MAO-B) inhibitor that increases dopamine availability in the striatum by blocking its catabolism. In early PD, selegiline monotherapy can provide symptomatic relief and may slow disease progression (though evidence for neuroprotection remains debated). It is particularly useful in younger patients or as adjunctive therapy with levodopa in advanced disease. Selegiline does not cause the motor side effects (dyskinesias, psychosis) associated with long-term dopamine agonists or levodopa, making it a rational first-line or early adjunct in PD management. The Indian standard of care (per NAMS guidelines and Harrison) supports MAO-B inhibitors as disease-modifying agents in early PD. Selegiline's selective inhibition of MAO-B (at therapeutic doses) avoids the tyramine interaction risk seen with non-selective MAOIs.
Why the other options are wrong
A. Donepezil — Donepezil is an acetylcholinesterase inhibitor used in Alzheimer's disease and Lewy body dementia to enhance cholinergic signaling. While PD patients may develop cognitive decline, donepezil does not address the dopamine deficit underlying motor symptoms (rigidity, tremor, bradykinesia). It is not a first-line or even adjunctive agent for motor PD. NBE trap: confusing cognitive symptoms in advanced PD with Alzheimer's pathology. B. Clozapine — Clozapine is an atypical antipsychotic used to manage psychosis in PD (e.g., hallucinations, delusions in advanced disease) without worsening parkinsonism, due to its weak dopamine D2 blockade and strong muscarinic antagonism. However, it does NOT treat the core motor features (rigidity, tremor). It is reserved for PD-related psychosis, not primary motor management. NBE trap: students may recall clozapine's unique role in PD and incorrectly select it for motor symptoms. C. Haloperidol — Haloperidol is a typical antipsychotic that blocks dopamine D2 receptors. In PD, haloperidol worsens rigidity, tremor, and bradykinesia by further reducing striatal dopamine. It is contraindicated in PD motor management and is used only in severe, refractory psychosis when atypical agents fail—and even then with caution. NBE trap: students may confuse antipsychotics as dopamine-related drugs and incorrectly assume they help PD.
High-Yield Facts
- Selegiline (MAO-B inhibitor): increases dopamine by blocking catabolism; used in early PD as monotherapy or adjunct to levodopa.
- Parkinson's triad: resting tremor, rigidity, bradykinesia; masked facies reflects loss of spontaneous facial movement.
- Selective MAO-B inhibition at therapeutic doses avoids tyramine interaction risk; non-selective MAOIs are contraindicated in PD.
- Clozapine is the only antipsychotic safe in PD psychosis; haloperidol and typical agents worsen motor symptoms.
- Donepezil addresses cognitive decline in advanced PD/Lewy body disease, not motor symptoms.
- Disease-modifying potential: selegiline may slow PD progression (DATATOP trial evidence), though neuroprotection remains debated in Indian practice.
Mnemonics
PD Motor Triad + Masked Facies TRaM: Tremor (resting), Rigidity, Masked facies (+ bradykinesia). Helps recall the cardinal signs that point to dopamine deficit. Antipsychotics in PD: CLOZAPINE SAFE, Others WORSEN CLOZ = safe (weak D2 blockade, strong anticholinergic). Haloperidol, risperidone, olanzapine = worsen parkinsonism. Use this to avoid the trap of giving typical antipsychotics. MAO-B Inhibitors: Selegiline & Rasagiline MARS: MAO-B inhibitors (Selegiline, Rasagiline) are selective, safe, and slow disease. Non-selective MAOIs = tyramine risk. Helps distinguish selegiline from other dopaminergic agents.
NBE Trap
NBE pairs "elderly patient with rigidity and tremor" with antipsychotics (clozapine, haloperidol) to lure students into confusing PD motor management with PD-related psychosis. The blank facies is a red herring—it is a motor sign, not a psychiatric symptom, and points to dopamine deficit, not dopamine excess.
Clinical Pearl
In Indian primary care and neurology clinics, selegiline is often started early in PD (especially in younger patients <60 years) to delay the need for levodopa and reduce long-term motor complications (dyskinesias, wearing-off). A patient presenting with the classic triad + masked facies should immediately trigger dopamine-enhancing therapy, not antipsychotics—a common pitfall in NEET PG exams.
_Reference: Harrison Ch. 428 (Parkinson's Disease); KD Tripathi Ch. 12 (Antiparkinsonian Drugs); Robbins Ch. 28 (Neurodegenerative Diseases)_