Pyomyositis Affecting the Paraspinal and Iliacus Muscles in a Patient With Staphylococcus aureus Urinary Tract Infection

We report a case of a 63-year-old man who presented with a four-day history of fever, night sweats, and left lower back pain, which radiated down to his left buttock and leg. He also had a short-lived episode of chest pain and breathlessness. He had a medical history of chronic back pain, which had been diagnosed as sciatica three years ago. Initial investigations revealed raised inflammatory markers due to a Staphylococcus aureus urinary tract infection. Despite treatment, his inflammatory markers did not improve and the left lower back pain persisted. A magnetic resonance imaging scan demonstrated features consistent with pyomyositis of the left lumbar erector spinae (paraspinal) and iliacus muscles. After prolonged antibiotic therapy, his symptoms completely resolved. Pyomyositis is a rare tropical infection of the skeletal muscles most commonly caused by Staphylococcus aureus. Risk factors include trauma and immunosuppression. This case highlights a nearly missed diagnosis of paraspinal and iliacus pyomyositis in patients with a background history of chronic lower back pain. Early diagnosis and treatment are pivotal in preventing serious complications such as septicemia and multi-organ failure.