One neuropathologic study showed that approximately one fourth of patients identified as having Parkinson's disease were incorrectly diagnosed. Neuroimaging is rarely useful in establishing the diagnosis, and because the diagnosis is made on the basis of clinical evidence, subspecialist consultation is frequently needed. Because all treatments are associated with significant side effects, therapy is usually deferred until patients have severe functional disability.
Many patients manage well without therapy for several years.
Levodopa therapy leads to dyskinesia and deterioration in approximately 10 percent of patients each year, but this rate is greater in younger patients. Selegiline was initially thought to be neuroprotective but was associated with an increased mortality rate in one large trial. Amantadine may improve dyskinesia but is less effective than levodopa and may cause confusion and skin disorders. Anticholinergics may relieve tremor, but these agents increase confusion and hallucinations in older patients and contribute to cognitive impairment in younger patients. New therapies based on dopamine agonists may provide effective monotherapy with acceptable side effects.