Cross sectional prevalence survey of idiopathic Parkinson's disease and parkinsonism in London

Subjects, methods, and results

Full details of the methods have been reported elsewhere.5 Records from 15 practices in London (121 608 patients) were screened for a diagnosis of Parkinson's disease or parkinsonism; antiparkinsonian drugs; or mention of tremor after the age of 50 years. Diagnosis was based on clinical assessment (by AS), with a video recording for secondary confirmation (by NPQ). Idiopathic Parkinson's disease was diagnosed according to the criteria of the UK Parkinson's Disease Society Brain Bank,^w1 with the exception that an isolated positive Babinski sign in an elderly patient with otherwise typical idiopathic Parkinson's disease was not considered to invalidate the diagnosis. Isolated classic resting tremor was considered to be “possible” Parkinson's disease. Multiple system atrophy and progressive supranuclear palsy were diagnosed according to published criteria.^{w2 w3} Vascular parkinsonism was diagnosed if at least two of the following were present: history of strokes, abrupt onset with stepwise progression, hypertension, a wide based gait with small steps, cognitive decline, pseudobulbar or pyramidal signs. Drug induced parkinsonism was diagnosed if a dopamine receptor blocking drug had been started within six months of the onset of symptoms and taken for at least six months. The date taken for calculating prevalence was 1 July 1997. We calculated crude prevalence rates and age adjusted rates by direct standardisation to the 1997 UK population, and a 95% confidence interval was calculated with Smith's method.^w4

Initial screening identified 679 patients, of whom 438 were excluded because they had drug induced parkinsonism, presented with dementia, or had no evidence of parkinsonism. Of the remaining 241 patients, 33 declined to participate and 6 died before they could be seen (response rate 84%). Probable or possible idiopathic Parkinson's disease was diagnosed in 156 patients (82 men) with a median age of 75 (range 34-94) years. Probable idiopathic Parkinson's disease was diagnosed in 152 of these patients and possible idiopathic Parkinson's disease in 4. More specific details about cases of multiple system atrophy and progressive supranuclear palsy and about atypical cases are reported elsewhere.5 Vascular parkinsonism was diagnosed in 17 patients, drug induced parkinsonism in 43 patients, and parkinsonism in 5 patients after the development of dementia. Of the 241 potential cases, 54 (22%) turned out not to have any form of parkinsonism.

The table shows the age specific and age adjusted prevalence rates for idiopathic Parkinson's disease and all types of parkinsonism. Rates increased with age and were greater for men than women in all age groups. The crude and adjusted rates for idiopathic Parkinson's disease (probable and possible combined) were 128 (95% confidence interval 109 to 150) per 100 000 and 168 (142 to 195) per 100 000 respectively. The corresponding rates for all types of parkinsonism were 193 (95% confidence interval 169 to 220) and 254 (95% confidence interval 222 to 287).

Comment

Prevalence of idiopathic Parkinson's disease in southern England seems to be remarkably similar to that in other areas of the United Kingdom reported by previous studies, suggesting no marked geographical variation. Prevalence has remained stable for 30 years despite decreasing mortality for patients aged under 75 years. Assuming that idiopathic Parkinson's disease remains undiagnosed in 10-20% of all community patients,^w5 the true prevalence of idiopathic Parkinson's disease in London may be around 200 per 100 000. These data are helpful for planning specialist services. The relatively high proportion of cases with an erroneous diagnosis of parkinsonism is of some concern and deserves further attention.