Unclassifiable parkinsonism in two European tertiary referral centres for movement disorders

In view of reports on high frequencies of atypical parkinsonism from different parts of the world and in non-white communities in the United Kingdom, we have prospectively surveyed 1,000 consecutive patients with parkinsonism presenting to two European tertiary referral centres for movement disorders (London, UK, and Barcelona, Spain). The aims of our study were to assess in a cross-sectional, prospective manner the proportion of patients who could not be classified diagnostically, to identify the factors precluding classification, and to determine which diagnostic measures would increase the rate of classifiable cases. Diagnoses were established using published clinical diagnostic criteria for Parkinson's disease (PD) and for other conditions associated with parkinsonism. Twenty-nine patients in London and 25 in Barcelona were initially considered unclassifiable; nine could be classified after further investigations. Levodopa (L-dopa) responsiveness was found to have a pivotal role in establishing a clinical diagnosis in previously unclassifiable patients: In those 45 patients who remained unclassifiable, failure to respond to L-dopa without other exclusion criteria for PD was the most common finding in each centre. Our results show that 4.0 to 5.0% of parkinsonian patients presenting to specialist clinics in Western Europe cannot be categorised using currently available clinical diagnostic criteria for parkinsonian syndromes. Prolonged follow-up and neuropathological diagnosis will be needed to determine whether all these cases represent atypical presentations of established clinico-pathological entities or whether some represent unrecognised new disorders.