A rare case report: Myopathy related to the interaction between azathioprine and infliximab in the treatment of ulcerative colitis and ankylosing spondylitis.

Key Clinical Message: Administering azathioprine or infliximab for UC and AS treatment carries a significant risk of adverse reactions. Here, we present the case diagnosed with UC and AS, who received treatment with azathioprine and infliximab for 10 months, and subsequently developed drug-induced myopathy affecting the right vastus medialis muscle.

Abstract: Drug-induced myopathy is an uncommon form of muscle injury that can arise in patients without preexisting muscle conditions when exposed to therapeutic doses of certain medications. Administering azathioprine or infliximab for ulcerative colitis (UC) and ankylosing spondylitis (AS) treatment carries a significant risk of adverse reactions, including drug-induced myopathy and increased susceptibility to opportunistic infections. However, occurrences of myopathy induced by the combination of azathioprine and infliximab are rarely reported in clinical practice. Here, we present the case of a 37-year-old male patient diagnosed with UC and AS, who received treatment with azathioprine and infliximab for 10 months. Despite the resolution of symptoms and improvement in intestinal mucosal inflammation observed via endoscopy, the patient subsequently developed drug-induced myopathy affecting the right vastus medialis muscle.