Rituximab and mepolizumab combination therapy for glucocorticoid-resistant myocarditis related to eosinophilic granulomatosis with polyangiitis

Eosinophilic granulomatosis with polyangiitis (EGPA), which belongs to the anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides, is characterised by eosinophil-rich granulomatous inflammation and small- to medium-sized vessel vasculitis associated with bronchial asthma and eosinophilia. It sometimes causes severe organ damage, of which myocardial damage is one of the most important for determining the prognosis. A case of EGPA-associated myocarditis that was refractory to glucocorticoid therapy and responded successfully to rituximab (RTX) and mepolizumab (MPZ) combination therapy is presented. A 46-year-old woman was diagnosed with EGPA-associated myocarditis due to pre-existing asthma, eosinophilia, mononeuritis multiplex, and eosinophilic myocarditis by myocardial biopsy. Transthoracic echocardiography showed thickening of the cardiac wall, pericardial effusion, and left ventricular hypokinesis. Although the myocarditis was refractory to methylprednisolone pulse therapy followed by oral high-dose prednisolone, the disease activity reached remission with the successful tapering of glucocorticoid after initiation of the RTX and MPZ combination therapy. Combination therapy with RTX and MPZ can be a good treatment option for EGPA-associated myocarditis for which it is difficult to give intravenous cyclophosphamide due to cardiac dysfunction.