When giant cell myocarditis affects only the atria.

I n this issue of Circulation, Larsen et al 1 report a new variant of giant cell myocarditis (GCM) with lone involvement of the atria and preserved left ventricular function. The diagnosis was supported not only by histology but also by cardiac magnetic resonance imaging showing atrial dilatation and wall thickening with marked edema, sparing the ventricles. The isolated atrial involvement was implicated as a cause of atrial fibrillation. The source of the atrial myocardial tissue for histological diagnosis of GCM was endomyocardial biopsy, surgery during maze procedure or valve intervention and bypass grafts, and autopsy. The distinctive histopathologic feature was the observation of giant cells and lymphocytic inflammatory infiltrates associated with cardiomyocyte necrosis, in the absence of caseous or noncaseous granulomas with epithelioid cells. This peculiar entity was sporadically reported in the past as case reports, 2–6 which are summarized altogether with the new observations in the form of review of the literature. 1 Atrial GCM is a novelty in the field of myocarditis, and the authors should be congratulated for their elegant contribution. GCM is an ominous life-threatening inflammatory cardio-myopathy with a severe prognosis. 7–9 GCM is also known with the eponym of Fiedler myocarditis, 10 since Schmorl (as reported by Saphir), 11 by reviewing the original hearts of the patients described by Fiedler and reported as isolated inter-stitial myocarditis, observed the presence of numerous giant cells. When GCM involves the ventricles, as usual, the clinical scenario is often that of cardiogenic shock attributable to abrupt pump failure, leading frequently to death unless averted by urgent intervention with ventricular assistance device or cardiac transplantation. The disease may even recur with a fatal outcome after transplantation. 12 Fortunately, the atrial variant of GCM appeared to be benign in this series reported by Larsen et al. 1 All 5 surviving patients, after treatment with corticosteroids and cyclosporine, returned to normal life after 1 to 4 months of follow-up; in 1 patient, who had a postmortem diagnosis, the cause of death was unrelated to GCM. The study raises some concerns which deserve consideration. Although the authors claim atrial GCM as a distinctive clinico-pathological entity, evidence of isolated atrial involvement is given by certainty only in 2 cases; 1 of them has a spectacular cardiac magnetic resonance, demonstrating marked isolated edema of the atrial walls and septum at the onset of the disease and isolated atrial fibrosis after treatment with high-dose corticosteroids …