[Mechanism, diagnosis, and treatment of steroid myopathy]

Steroid myopathy, characterized by muscle atrophy and weakness, is an adverse effect of high-dose steroid therapy. Weakness of proximal muscle that interferes with activities of daily living is a serious problem for patients with steroid myopathy. Here, we outline the pathogenic mechanism, diagnosis, and treatment of steroid myopathy. Recent studies have shown that steroid-mediated induction of ubiquitin ligases (atrogin-1, muscle RING finger-1) and suppression of mammalian/mechanistic target of rapamycin cause an imbalance between anabolism and catabolism of muscle proteins, resulting in muscle atrophy. Despite the progress in understanding the pathogenic mechanism, the diagnosis and treatment of steroid myopathy has not yet been established. Small changes in muscle enzymes, including CK, LDH, and aldolase, make it difficult to define diagnostic criteria. Furthermore, since there is no drug available for treating the disorder, the patients have no opinion except waiting for spontaneous recovery with steroid tapering and exercising. To address these issues, we introduce novel approaches involving branched-chain amino acids that aim at treatment and assessment of steroid myopathy.