Which motor symptom is characteristic of Parkinson's disease?

• A. Tremor at rest.
• B. Severe claustrophobia.
• C. Limb jerks only during voluntary movement.
• D. Tremor exclusively on movement.

Answer: (A)

Resting tremor is a hallmark motor feature of Parkinson's disease. It appears when the affected muscles are at rest and typically diminishes or disappears with voluntary movement. This tremor, often described as a pill-rolling motion of the hand, reflects dysfunction in basal ganglia circuits due to loss of dopaminergic neurons in the substantia nigra. In the broader picture, Parkinson’s motor signs include bradykinesia and rigidity as well, but the resting tremor is the classic and most recognizable early feature.

The other possibilities don’t fit the pattern: severe claustrophobia is an anxiety symptom, not a motor sign of Parkinson’s; limb jerks only during voluntary movement point to different movement disorders like myoclonus; tremor that occurs exclusively during movement is an intention tremor, which is typical of cerebellar disorders.