**Question:** Characteristic pathological feature of Parkinson's disease is presence of -

A. Protein aggregation
B. Lewy bodies
C. Neuronal loss
D. Depression

**Core Concept:**
Parkinson's disease is a progressive neurodegenerative disorder characterized by motor symptoms like tremors, rigidity, bradykinesia, and postural instability. The primary pathological finding in Parkinson's disease is the accumulation of misfolded proteins, particularly alpha-synuclein, which forms Lewy bodies within the affected neurons.

**Why the Correct Answer is Right:**
B. Lewy bodies are protein aggregates composed of misfolded alpha-synuclein that accumulate within the neurons of the substantia nigra, a region in the brain responsible for motor control. This accumulation leads to neuronal dysfunction and death, contributing to the motor symptoms of Parkinson's disease.

**Why Each Wrong Option is Incorrect:**
A. Protein aggregation is a general term that applies to Parkinson's disease but does not specifically describe the key pathological feature.
C. Neuronal loss occurs in Parkinson's disease, but the correct answer is Lewy bodies, as they directly cause neuronal dysfunction and death.
D. Depression is a non-motor symptom of Parkinson's disease, while the question asks about the pathological feature.

**Clinical Pearl:**
The presence of Lewy bodies in affected neurons is a critical feature to differentiate Parkinson's disease from other movement disorders like essential tremor and multiple system atrophy, which share similar motor symptoms but lack this specific pathological hallmark.

**Correct Answer:** B. Lewy bodies