Sensitivity and specificity of cardiac metaiodobenzylguanidine scintigraphy in the early diagnosis of Parkinson's disease.

PURPOSE: Metaiodobenylguanidine (MIBG) scintigraphy has been shown to enhance the probability of correct diagnosis in patients with parkinsonian syndromes (PS). Thus far, studies of the clinical usefulness of MIBG have been confined to cross-sectional assessments, which are inevitably associated with diagnostic uncertainty during the early stages of these syndromes. In this study, the initial clinical diagnosis was reevaluated longitudinally to assess the sensitivity and specificity of clinical and MIBG parameters in the early diagnosis of PS.
METHODS: 167 patients with PS (age 67.03 ± 8.92 years (mean ± standard deviation), duration of symptoms 2.48 ± 5.27 years, median Hoehn and Yahr score 2) underwent an initial clinical assessment and MIBG scintigraphy. Eighty seven of those patients (56 with Parkinson's disease (PD), 1 with multiple system atrophy (MSA), 23 with atypical PS, 7 with tremor syndrome) were clinically reevaluated a mean of 3 years later in order to verify their initial diagnosis.
RESULTS: The use of a lower limit of normal value of 1.74 for the heart-to-mediastinum ratio (HMR) achieved the best discrimination between PD and other PS. The sensitivity of MIBG scintigraphy to PD was 94%; it also had a specificity of 65%, a positive predictive value of 88%, and a negative predictive value of 79%. MIBG scintigraphy was better than initial clinical diagnosis alone (sensitivity 83%, specificity 39%) or levodopa responsiveness (sensitivity 92%, specificity 10%). However, a combination of clinical diagnosis and MIBG scintigraphy was found to be especially clinically useful (specificity 95%, sensitivity 83%, positive predictive value 95%, negative predictive value 83%).
CONCLUSION: MIBG scintigraphy was demonstrated to be a reliable tool for the diagnosis of early PD. The best diagnostic accuracy was achieved by combining a clinical examination with MIBG scintigraphy.