Gallium-67 imaging in patients with dilated cardiomyopathy and biopsy-proven myocarditis

Current standard for detection of myocarditis in a clinical setting rely on endomyocardial biopsy for accurate diagnosis. With this technique a subset of patients with dilated cardiomyopathy show unsuspected myocarditis histologically. Endomyocardial biopsy, despite its specificity, may lack sensitivity due to sampling error if the inflammation is patchy or focal. Therefore, inflammation-sensitive radioisotopic imaging may be a useful adjunct in the diagnosis of myocarditis. This study was designed to evaluate the applicability of gallium-67 (⁶⁷Ga) myocardial imaging as an adjunct to endomyocardial biopsy in the diagnosis of myocarditis. Sixty-eight consecutive patients referred for evaluation of dilated cardiomyopathy underwent 71 parallel studies with ⁶⁷Ga imaging and biopsies that served as the basis of comparison for this study. Histologic myocarditis was identified in 8% of biopsy specimens. Clinical and hemodynamic parameters could not be used to predict the presence of myocarditis. Five of six samples (87%) with myocarditis showed dense ⁶⁷Ga uptake, whereas only nine of 65 negative biopsy samples (14%) were paired with equivocally positive ⁶⁷Ga scans (p < .001). The single patient with myocarditis and no myocardial ⁶⁷Ga uptake had dense mediastinal lymph node uptake that may have obscured cardiac uptake. The incidence of myocarditis on biopsy with a positive ⁶⁷Ga scan was 36% (5/14); however, the incidence of myocarditis with a negative ⁶⁷Ga scan was only 1.8% (1/57). Follow-up scans for three patients showed close correlation of ⁶⁷Ga uptake with myocarditis on biopsy. In conclusion ⁶⁷Ga may be a useful screening test for identifying patients with a high yield of myocarditis on biopsy, and serial scans may eliminate the need for frequent biopsies in patients with proven myocarditis.