On examination of an adult patient, which combination of signs is most consistent with Parkinson's disease?

• A. Parkinson's disease
• B. Depression
• C. Drug induced reaction
• D. Functional impairment

Answer: (A)

Think about the motor pattern that defines Parkinson's disease. The classic Parkinsonian syndrome is built around a triad of features seen on exam: a resting tremor (often a pill-rolling tremor when the limb is at rest), bradykinesia (slowness of movement, affecting finger taps, gait, and overall spontaneous action), and rigidity (increased muscle tone with a lead-pipe or cogwheel feel). Postural instability tends to appear as the disease progresses. When you encounter an adult with these signs together, they point most strongly to Parkinson's disease because they reflect the loss of dopaminergic neurons in the nigrostriatal pathway and the resulting disruption of dopamine modulation in the basal ganglia.

Depression can cause psychomotor slowing and fatigue, but it normally lacks the hallmark resting tremor and rigidity that PD produces. A drug-induced reaction (parkinsonism) can mimic PD with tremor and rigidity, but it usually follows exposure to a causative medication and may improve after stopping the drug. Functional impairment is a broad, non-specific descriptor that doesn't explain the distinctive motor features of Parkinson's.

So, the constellation of resting tremor, bradykinesia, and rigidity on exam best fits Parkinson's disease.