A Severe Steroid‐Induced Myopathy in a Child With a Pharmacogenetic Predisposition: A Case Report and Systematic Review of the Literature

BACKGROUND: Glucocorticoids (GCs) are essential in paediatric inflammatory and immune-mediated diseases but are associated with dose- and duration-dependent toxicity. Pharmacogenetic variability in metabolic and transporter pathways may contribute to inter-individual differences in GC adverse effects. CASE PRESENTATION: A 7-year-old girl with recurrent IgA vasculitis required prolonged corticosteroid therapy. During treatment, she developed marked Cushingoid features, progressive proximal muscle weakness, and severe fatigability consistent with steroid-induced myopathy. Pharmacogenetic analysis revealed a CYP3A4 intermediate metabolizer genotype and CYP3A5 poor metabolizer genotype, without relevant variants in ABCB1 or ABCG2. NLRP3 methylation analysis was normal. Gradual steroid tapering combined with intravenous immunoglobulin therapy resulted in rapid clinical improvement and sustained remission. METHODS AND RESULTS: A systematic review of PubMed, Embase, and Scopus up to March 2026 identified seven eligible studies. Evidence on associations between CYP3A4, CYP3A5, ABCB1, and ABCG2 polymorphisms and GC-related adverse effects in children was limited and inconsistent, without strong genotype-phenotype correlations. CONCLUSIONS: This case suggests that combined CYP variants may contribute to increased glucocorticoid exposure and side effects. Although current evidence remains insufficient for routine clinical use, pharmacogenetic testing may be considered in selected cases with unexpected GC adverse effects.