Long-Term Outcome and its Predictors in Giant Cell Myocarditis. Letter Regarding the Article ‘Long-Term Outcome and its Predictors in Giant Cell Myocarditis’

In 2016, we reported in your Journal1 on the outcome of 46 patients with giant cell myocarditis (GCM) in Finland. Later, we encountered incidental cases of GCM where the diagnosis was converted to cardiac sarcoidosis (CS) at post-transplant or post-mortem examinations. This forced us to re-evaluate all GCM diagnoses made since 1991 in our country.2 Altogether 26 of the 46 cases were reclassified as CS, most commonly due to recognition, with help of immunochemistry, of sarcoid granulomas missed or misinterpreted on original microscopy (Figure 1). The 5-year estimate (95% confidence interval) of transplant-free survival, having been 42% (39–56%) in our 2016 report,1 was 25% (0–40%) in the 20 patients keeping the GCM diagnosis. In Cox regression analysis involving all 46 patients, GCM predicted the occurrence of death or transplantation with a hazard ratio (95% confidence interval) of 2.68 (1.22–5.87, P = 0.014). In bivariate Cox analyses, biomarkers of cardiac injury and dysfunction, as well as at least moderate myocardial necrosis or fibrosis, predicted the outcome independent of the diagnosis of CS or GCM. The hazard ratios are shown in Table 1. Cardiac sarcoidosis and GCM are known to share clinical manifestations and characteristics of histopathology.3-5 Their differentiation on microscopy of tiny endomyocardial samples can be very difficult, sometimes nearly impossible. Magnetic resonance imaging and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography can be of some help as mediastinal lymphadenopathy and 18F-FDG uptake suggest CS and mediastinal lymph node biopsy may expose sarcoidosis histology. Distinction of CS and GCM is complicated further by the fact that researchers divide on the diagnostic role of myocardial granulomas. Some, like us, consider granulomas and GCM mutually exclusive2-4 but others disagree.5 It is also possible that CS and GCM are not fully different entities but intimately related diseases or even partially overlapping segments of a single disease spectrum. The reader who favours their dichotomy should know, however, that the study population of our 2016 paper1 was a mix of CS and GCM by our current criteria and that the lower 5-year survival estimate reported here better represents true GCM.