What are main symptoms of Parkinson's disease?

• A. Tremor and mood swings.
• B. Bradykinesia and memory loss.
• C. Tremor, rigidity, bradykinesia, postural instability.
• D. Hallucinations and delusions.

Answer: (C)

Parkinson's disease is defined by loss of dopamine-producing neurons in the substantia nigra, which disrupts basal ganglia circuits and produces slowed movement and stiffness. The main motor features, known as the four cardinal signs, are tremor at rest, muscular rigidity, bradykinesia (slowness of movement), and postural instability (impaired balance). This full quartet captures the core motor presentation of the disease, making it the best choice. Tremor with mood swings or bradykinesia with memory loss miss at least one of these defining motor signs, and hallucinations or delusions are non-motor symptoms more related to psychosis or other conditions rather than the primary motor phenotype.