Diagnostic cutoff points for ¹²³I-MIBG myocardial scintigraphy in a Caucasian population with Parkinson's disease

Abstract

Purpose: Molecular imaging with (123)I-metaiodobenzylguanidine (MIBG) has been used in Parkinson's disease (PD), but there is no consensual index to discriminate between normal and PD patients in the Caucasian population. The purpose of this study was to determine diagnostic cutoff points in the quantification of MIBG cardiac uptake in our population of PD patients. We have also calculated the reproducibility over a range of interpretation expertise.

Methods: The study included 14 PD patients and 14 normal age- and sex-matched controls. Heart to mediastinum ratios (H/M) were calculated at 15 min (H/M15m) and 4 h (H/M4h) post-injection by three observers with different interpretation expertise, one of whom drew the regions of interest at three different times. The intraobserver and interobserver reliability was calculated (interclass correlation coefficient and coefficient of variability). Diagnosis was estimated by maximizing the Youden index for H/M and washout ratios. Discrimination ability was assessed by the area under the curve (AUC). Sensitivity and specificity were reported, using our thresholds.

Results: The parameter with the best diagnostic accuracy was the H/M4h ratio, with a major AUC (0.976 area under the receiver-operating characteristic curve). The threshold was 1.43 with a 95% confidence interval of 1.37-1.50. Using this threshold, the sensitivity and specificity were 93 and 100%. The interobserver and intraobserver variabilities measuring this ratio were 3.2 and 3.1%, respectively.

Conclusion: The diagnostic cutoff point for (123)I-MIBG myocardial scintigraphy in a Caucasian population with PD was 1.43 for the H/M4h index, with a good sensitivity and specificity. The technique is easy to use, with a good reproducibility over a range of interpretation expertise.