A breast cancer patient with chemotherapy-induced chronic lymphocytic myocarditis successfully treated with steroid...

A 63-year-old female patient with a history of postoperative recurrence of breast cancer after radiation therapy underwent chemotherapy with epirubicin (total 960 mg) and low-dose cyclophosphamide. She developed acute decompensated heart failure with reduced ejection fraction. Despite initial treatment with diuretics and inotropic drugs, her condition worsened, leading to low-output syndrome and frequent paroxysmal atrial fibrillation (AF). The patient underwent an endomyocardial biopsy and catheter ablation for AF. The endomyocardial biopsy revealed predominant lymphocyte invasion rather than cardiomyocyte injury, indicating drug-induced chronic lymphocytic myocarditis. The clinical course and biopsy findings indicated that other potential causes were unlikely, such as viral infection, collagen disease, and immune checkpoint inhibitor use. Following steroid pulse therapy, maintenance therapy with a starting dose of 80 mg of methylprednisolone (mPSL) led to a significant improvement in hemodynamics, resulting in her discharge on the 82nd day with an improved ejection fraction from 20 % to 42 %. A second endomyocardial biopsy under 20 mg of mPSL showed a marked improvement in lymphocytic infiltration. This case serves to illustrate the significance of endomyocardial biopsy in the context of refractory heart failure with an onco-cardiology case, whereby an appropriate diagnosis can be made and successful steroid therapy can be initiated.

Although heart failure after chemotherapy is frequently reported, reports of chronic lymphocytic myocarditis after chemotherapy are relatively uncommon. Endomyocardial biopsy has enabled the differential diagnosis of cardiac toxicity and has led to the diagnosis of lymphocytic myocarditis. Currently, the optimal treatment for chronic lymphocytic myocarditis remains unestablished. However, in this case, it was found that steroid therapy was effective.