Pyomyositis in childhood-systemic lupus erythematosus.

Pyomyositis is a pyogenic infection of skeletal muscle that arises from hematogenous spread and usually presents with localized abscess. This muscle infection has been rarely reported in adult-onset systemic lupus erythematous and, to the best of our knowledge, has not been diagnosed in pediatric lupus population. Among our childhood-onset systemic lupus erythematous population, including 289 patients, one presented pyomyositis. This patient was diagnosed with childhood-onset systemic lupus erythematous at the age of 10 years-old. After six years, while being treated with prednisone, azathioprine and hydroxychloroquine, she was hospitalized due to a 30-day history of insidious pain in the left thigh and no apparent trauma or fever were reported. Her physical examination showed muscle tenderness and woody induration. Laboratory tests revealed anemia, increased acute phase reactants and normal muscle enzymes. Computer tomography of the left thigh showed collection on the middle third of the vastus intermedius, suggesting purulent stage of pyomyositis. Treatment with broad-spectrum antibiotic was initiated, leading to a complete clinical resolution. In conclusion, we described the first case of pyomyositis during childhood in pediatric lupus population. This report reinforces that the presence of localized muscle pain in immunocompromised patients, even without elevation of muscle enzymes, should raise the suspicion of pyomyositis. A prompt antibiotic therapy is strongly recommended.