Yersinia pseudotuberculosis-Associated Myositis.

Yersinia pseudotuberculosis (Y. pstb.) is a Gram-negative pathogen associated with gastrointestinal infections, such as enterocolitis. While complications like reactive arthritis can occur, progression to myositis is extremely rare. This report describes a five-year-old boy who developed myositis following a Y. pstb. infection. The patient presented with a five-day history of abdominal pain, fever, and leg pain that progressed to muscle weakness, which affected his ability to walk. Laboratory results showed elevated inflammatory markers, and stool cultures confirmed Y. pstb. infection. Magnetic resonance imaging (MRI) examination revealed muscle inflammation consistent with myositis. The patient improved rapidly with conservative treatment (rest and acetaminophen) and did not require antibiotics. Thirteen years later, he remained asymptomatic. This case highlights the rare complication of myositis following Y. pstb. infection. Potential mechanisms include postinfectious immune-mediated myositis. Clinicians should be aware of this possibility, and conservative treatment may suffice for recovery.