Clinical Implications of Cardiac-MIBG SPECT in the Differentiation of Parkinsonian Syndromes

BACKGROUND AND PURPOSE (123)I cardiac meta-iodobenzylguanidine (MIBG), an analogue of norepinephrine, has been used to estimate myocardial sympathetic nerve function. We investigate whether cardiac-MIBG SPECT is clinically applicable in the differentiation of Parkinson's disease (PD) from parkinsonian syndromes. METHODS Cardiac-MIBG scintigraphy was performed in 27 controls, in 40 patients with PD and in 52 patients with other parkinsonian syndromes comprising 23 with multiple system atrophy (MSA), 26 with drug-induced parkinsonism (DIP), and 3 with corticobasal degeneration (CBD). The heart to mediastinum (H/M) uptake ratio was calculated for each subjects. Patients who either had medical conditions that confused the MIBG SPECT results or who took medications that interfere with MIBG accumulation were excluded from the study. RESULTS Both early and delayed H/M ratios were in patients with PD significantly lower than in controls (early, 1.34+/-0.15 vs 1.79+/-0.19; delayed, 1.29+/-0.15 vs 2.06+/-0.29, p<0.001). In patients with PD, both early and delayed H/M ratios were significantly lower than those in patients with MSA (early, 1.68+/-0.23; delayed, 1.80+/-0.34, p<0.001), DIP (early, 1.83+/-0.24; delayed, 2.07+/-0.4, p<0.001), or CBD (early, 1.85+/-0.01; delayed, 1.99+/-0.19, p<0.001). Two patients with DIP, who were within the range of patients with PD, showed clinically similar courses of PD. CONCLUSIONS This study demonstrates that cardiac-MIBG is a clinically powerful tools to differentiate PD from other parkinsonian syndromes.