BACKGROUND Peripherally inserted central catheters (PICCs) are commonly used by clinicians in daily practice as a safe and reliable alternative to central venous catheters. While there are advantages to the use of PICCs, such as a low insertion-related complication rate and cost-effectiveness, using PICCs may expose patients to life-threatening severe complications such as a central line-associated bloodstream infection and deep venous thrombosis (DVT). There have been no reports of infectious myositis associated with PICC insertion. CASE REPORT We report a case of infectious myositis related to PICC insertion complicated by brachial DVT in a 43-year-old immunocompromised patient with myelodysplastic syndrome. Despite the administration of broad-spectrum antibiotics, the patient's condition did not improve. He developed septic shock and required emergency excision of the infected and necrotic muscles. Although the pathogen responsible for the infection was unknown, infectious myositis and myonecrosis were observed intraoperatively. Furthermore, histopathological examination revealed evidence of infectious myositis in the biceps brachii and brachial muscles. The septic shock resolved with treatment and the patient survived with residual elbow joint dysfunction. CONCLUSIONS We present a case of infectious myositis related to PICC insertion. We believe that urgent resection of infected and necrotic tissues, rather than broad-spectrum antimicrobial therapy alone, was essential to save the patient's life.