Matthew A. Menza, MD

Parkinson disease (PD) is the second most common neurodegenerative illness in the United States, affecting more than 1 million persons. Disease onset is usually after age 50. In persons older than 70 years, the prevalence is 1.5% to 2.5%.1 While the primary pathology involves degeneration of dopaminergic neurons in the substantia nigra, circuits important in emotion and cognition-such as the serotonergic, adrenergic, cholinergic, and frontal dopaminergic pathways-are also variably disrupted.