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Overdiagnosis of Parkinson's disease (PD) is suggested by specialist review of community diagnosis, and in postmortem studies. In specialist centers 4 to 15% of patients entered into clinical trials as early PD do not have functional imaging support for a PD diagnosis. In a European multicenter, prospective, longitudinal study, we compared clinical diagnosis with functional SPECT imaging using [123I]FP-CIT (DaTSCAN, GE Healthcare). Repeat observations were performed over 3 years in patients with tremor and/or parkinsonism in whom there was initial diagnostic uncertainty between degenerative parkinsonism and nondegenerative tremor disorders. Video-recording of clinical features was scored independently of functional imaging results by two blinded clinicians at 36 months (= gold standard clinical diagnosis). Three readers, unaware of the clinical diagnosis, classified the images as normal or abnormal by visual inspection. The main endpoint was the sensitivity and specificity of SPECT imaging at baseline compared with the gold standard. In 99 patients completing the three serial assessments, on-site clinical diagnosis overdiagnosed degenerative parkinsonism at baseline in diagnostically uncertain cases compared with the gold standard clinical diagnosis (at 36 months), the latter giving a sensitivity of 93% and specificity of 46%. The corresponding baseline [123I]FP-CIT SPECT results showed a mean sensitivity of 78% and a specificity of 97%. Inter-reader agreement for rating scans as normal or abnormal was high (Cohen's kappa = 0.94-0.97).

To record prospectively, from early presentation, the clinical features of parkinsonism and tremor disorders, in relation to evidence of dopaminergic deficit shown with [(123)I]-FP-CIT (DaTSCAN, Amersham Health) single photon emission computerised tomography (SPECT). Clinical signs were recorded in 62 patients, of whom 24 failed standard Parkinson's disease (PD) and essential tremor criteria, and 38 fulfilled UK Brain Bank step 1 PD criteria. Striatal radioligand uptake was graded visually as normal or abnormal, and specific:nonspecific ratios were calculated. Bradykinesia and rigidity showed significant overall association with abnormal scans (P < or = 0.003), but rest tremor did not (P = NS). In the 24 patients not fulfilling specific criteria (mean age 63 [SD 9] years, disease duration 3 [SD 4] years), 10 (42%) had abnormal visual SPECT assessment and 14 (58%) had normal scans. Of 38 patients with early PD by clinical criteria (mean age 60 [SD 9] years, disease duration 3 [SD 1.7] years), 33 (87%) were visually abnormal. Baseline clinical diagnosis corresponded with SPECT imaging results in 51 of 62 cases (82%), which increased to 56 of 62 cases (90%) with amendment of seven clinical diagnoses at 3 months (blind to SPECT results). Akinetic-rigid cardinal diagnostic features of parkinsonism associate well with dopaminergic deficit in patients with early and mild clinical features. When these clinical features are uncertain, or the patient fails clinical diagnostic criteria, testing for dopaminergic deficit with [(123)I]-FP-CIT SPECT may assist the diagnostic process.