We read with interest the report by Lewis et al 1 on clinical heterogeneity of Parkinson’s disease based on a data driven approach. In their cohort of patients with Parkinson’s disease they identified different subgroups within their population, including those with relatively early onset, those with a tremor dominant subtype, those with non-tremor dominant subtype with cognitive impairment and mild depression, and those with rapid progression without cognitive impairment. We undertook a similar analysis—which was originally conducted before the publication by Lewis et al —in a previous community based prevalence study in the London area, the details of which are described elsewhere.2 The clinical features of 124 patients with previously proposed clinical subtypes of Parkinson’s disease were compared, and a cluster analysis entering all variables that had differed between these groups undertaken. Age at onset, current age, presence of dementia, fluctuations, dyskinesia, and rate of progression all differentiated patients within this sample of individuals with …