What is a common symptom of Parkinson's disease that may be managed with diphenhydramine?

Tremors are a classic symptom of Parkinson's disease and occur due to the loss of dopamine-producing neurons in the brain, which disrupts normal movement control. Diphenhydramine, an antihistamine, is sometimes used to provide symptomatic relief for certain types of movement disorders, including tremors. While not a first-line treatment for Parkinson's, diphenhydramine can have some efficacy in managing these symptoms, particularly in cases where tremors are exacerbated by other factors, such as medications that induce side effects resembling those of Parkinson's.

The other symptoms listed do not align with the primary management focus of diphenhydramine in Parkinson's disease. Severe headaches might require analgesics or other interventions rather than an antihistamine. Loss of appetite can be addressed through dietary intervention or appetite stimulants, and blurred vision is often managed through adjustments in lighting, glasses, or other eye care treatments. Therefore, tremors are the symptom most closely associated with the potential benefit of diphenhydramine in the context of Parkinson's disease management.