In addition to the classic symptoms of Parkinson's, what is another common feature of the disease?

Decreased olfactory function is a recognized non-motor symptom of Parkinson's disease. Many patients experience a diminished sense of smell, known as hyposmia or anosmia, which often occurs early in the disease process, sometimes even before the classic motor symptoms of tremors, rigidity, and bradykinesia appear. This symptom can be distressing for patients and serves as one of the potential biomarkers for the disease, aiding in early diagnosis.

In contrast, the other options do not hold the same association with Parkinson's disease. For example, increased appetite and hyperactivity are generally not features of Parkinson's; rather, patients often experience changes in appetite and may become less active as the disease progresses. Visual hallucinations can occur in some patients with Parkinson's, especially those who are on dopaminergic medications, but they are not as universally present or as early in the disease process as decreased olfactory function. Thus, the recognition of decreased olfactory function as a common feature of Parkinson's underscores its significance in the comprehensive understanding and management of the disease.