The detection of preclinical Parkinson's disease: what is the role of positron emission tomography?

On clinical criteria alone, the diagnosis of early Parkinson's disease can be difficult and, by definition, the prospective recognition of preclinical Parkinson's disease is impossible. Positron emission tomography (PET) using [18F]dopa as tracer has been proposed as a means of identifying patients with preclinical disease. The number of subjects detected to date has been few; most have been identified by serendipity or during the course of family studies. This review examines the significance of a single abnormal scan in an apparently healthy subject in terms of the relationship between normal and abnormal values and the time course of the disease.