Prevalence of progressive supranuclear palsy and multiple system atrophy: a cross-sectional study.

BACKGROUND: The prevalence of progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) in the general population is unknown. Clinicopathological studies of patients diagnosed as having Parkinson's disease suggest that the two disorders may be underdiagnosed. We investigated the population prevalence of these disorders.

METHODS: We screened computerised records of 15 general practices in London, UK, for patients with specific diagnostic labels suggestive of Parkinson's disease or parkinsonism and all patients who had ever received antiparkinsonian medication. We assessed eligible patients by review of records, interview, physical examination, and video recordings of neurological signs for independent diagnostic confirmation. We diagnosed parkinsonian disorders according to published criteria and further reviewed patients with atypical features after 1 year.

FINDINGS: The participation rate was 84%. The age-adjusted prevalence for PSP was 6.4 per 100,000 (five probable and one possible case [95% CI 2.3-10.6]) and for MSA 4.4 per 100,000 (two probable and two possible cases [1.2-7.6]). An additional four atypical patients were identified at 1 year but did not fulfil criteria for PSP or MSA.

INTERPRETATION: Our results suggest that the true prevalence of PSP and MSA has been underestimated, since many patients in the community remain undiagnosed or misdiagnosed.