Successful high-dose glucocorticoid therapy for anti-mitochondrial antibody-positive myocarditis arising during tocilizumab and low-dose glucocorticoid therapy for rheumatoid arthritis.

Anti-mitochondrial antibody (AMA)-positive myopathy, a recently identified condition with significant cardiac involvement, poses a serious challenge in treatment consensus due to its extreme rarity. While several studies demonstrate the efficacy of high-dose prednisolone in managing this disease, the current literature lacks substantial evidence regarding the effectiveness of biologic therapy or low-dose prednisolone for remission induction. Here, we present a case of AMA-positive myocarditis that emerged during rheumatoid arthritis treatment with tocilizumab (TCZ) and low-dose prednisolone (PSL). Successfully, intensive immunosuppressive therapy with high-dose PSL proved effective in stabilizing this condition. Our case highlights the necessity of a robust immunosuppressive approach, favoring high-dose PSL over the combination of low-dose PSL and TCZ in this disease.