Relation of iodine-123 metaiodobenzylguanidine myocardial scintigraphy to endomyocardial biopsy findings in patients with dilated cardiomyopathy

Background: Iodine-123 metaiodobenzylguanidine (¹²³I-MIBG) concentrates in adrenergic neurons and has been developed for evaluation of the sympathetic nervous system. Recent studies have demonstrated that the normal heart is clearly visualized by ¹²³I-MIBG cardiac scintigraphy, whereas abnormal ¹²³I-MIBG myocardial uptake and washout have been demonstrated in patients after myocardial infarction and in patients with congestive cardiomyopathy, long QT syndrome, and ventricular tachycardia. Hypothesis: Based on evidence from recent studies, it can be hypothesized that ¹²³I-MIBG uptake is related to histopathologic changes in the myocardium. Methods: The relation of ¹²³I-MIBG uptake to the histologic findings for the heart was studied in 24 patients with dilated cardiomyopathy (DCM). The study group did not include patients with complicating disorders that primarily affect the adrenergic nervous system. The ¹²³I-MIBG uptake was visually assigned one of four grades using the two criteria of the mean score for six regional uptake grades (mean score) and the global score obtained by visual evaluation of the entire image (global score). The ¹²³I-MIBG uptake score was also determined for the region at which the biopsy specimen was obtained (biopsy region score). The histologic findings were evaluated by assigning one of four grades for each of the following five factors: myocyte hypertrophy, myocardial fibrotic change, myocyte degeneration and necrosis, mononuclear cell infiltration, and myocyte disarray. The sum for all grades was defined as the total score, and the global score was also assigned to the overall histologic findings. Results: All of the global, mean, and biopsy region scores for ¹²³I-MIBG uptake correlated significantly with the global and total scores for the histologic findings. Among the histologic factors, myocyte degeneration showed score correlated with all global, mean, and biopsy region scores for the uptake. Myocyte hypertrophy was associated weakly with the ¹²³I-MIBG uptake scores. Conclusion: These results indicate that ¹²³I-MIBG uptake imaging is associated with histopathologic abnormalities in patients with DCM.