123I-MIBG cardiac uptake and smell identification in parkinsonian patients with LRRK2 mutations

Abstract

Reduced uptake of (123)I- metaiodobenzylguanidine (MIBG) on cardiac gammagraphy and impaired odor identification are markers of neurodegenerative diseases with Lewy bodies (LB) as a pathological hallmark, such as idiopathic Parkinson's disease (IPD). LRRK2 patients present with a clinical syndrome indistinguishable from IPD, but LB have not been found in some cases. Patients with such mutations could behave differently than patients with IPD with respect to MIBG cardiac uptake and olfaction. We studied 14 LRRK2 patients, 14 IPD patients matched by age, gender, disease duration and severity, and 13 age and gender matched control subjects. Olfaction was analyzed through the University of Pennsylvania Smell Identification Test (UPSIT). MIBG cardiac uptake was evaluated through the H/M ratio. The late H/M was 1.44 ± 0.31 for LRRK2 patients, 1.19 ± 0.15 for PD patients, and 1.67 ± 0.16 for control subjects. LRRK2 patients presented lower but not statistically significant MIBG cardiac uptake than controls (p = 0.08) and significant higher uptake than PD patients (p = 0.04). UPSIT mean scores were 21.5 ± 7.3 for LRRK2 patients, 18.7 ± 6.2 for IPD patients and 29.7 ± 5.7 for control subjects. UPSIT score was lower in both LRRK2 and PD than in controls. In LRRK2 patients a positive correlation was found between myocardial MIBG uptake and UPSIT scores, (R = 0.801, p < 0.001). In LRRK2 patients, MIBG cardiac uptake was less impaired than in PD; a positive correlation between MIBG cardiac uptake and UPSIT scores was observed. As MIBG cardiac reduced uptake and impaired odor identification are markers of LB pathology, this findings may represent neuropathological heterogeneity among LRRK2 patients.

Fig. 1

Scatter plot showing early (a) and late (b) H/M ratios for ¹²³I-MIBG cardiac uptake in patients with idiopathic Parkinson’s disease (IPD), patients with parkinsonism and LRRK2 mutations (LRRK2-PD) and controls. Circles represent individual values; the bar refers to the mean H/M ratio in each group

Fig. 2

Relationship between early (a) and delayed (b) H/M ratio for ¹²³I-MIBG cardiac uptake and UPSIT scores in patients with parkinsonism and LRRK2 mutations. (Early: R = 0.62 p < 0.02; late: R = 0.68 p = 0.01)

Fig. 3

UPSIT scores of patients with normal and abnormal delayed MIBG ratios