Multifocal pyomyositis after intra‐articular injections

An 82yearold female who had received injections of hyaluronic acid into her knee joints several times because of osteoarthritis was admitted to a local hospital because of fever. Methicillinsusceptible Staphylococcus aureus was detected from cultures of blood and kneejoint fluid. Cefazolin administration was initiated. However, her condition did not improve for 3 weeks, so she was transferred to our hospital. She could not sit down because of systemic pain, but focal signs were absent. Computed tomography demonstrated multiple abscesses in trapezius (Figure 1A), triceps (B), iliopsoas (C), erector spinae (C), and quadriceps (D) muscles that extended around the hip joint and pubic bone. She was diagnosed with multifocal pyomyositis due to S. aureus. Management comprised surgical drainage and antibiotic administration for a long period. Pyomyositis is a pyogenic infection of the larger skeletal muscles and is usually accompanied by abscess formation. Pyomyositis is usually endemic in countries with tropical climates, but has been recognized with increasing frequency in temperate climates.1 Pathogenesis of pyomyositis is not known. Skeletal muscle is usually resistant to bacterial infection. Experimental injection of S. aureus into the leg muscles of dogs or intravenous injection of S. aureus does not result