Primary Pyomyositis as Unusual Cause of Limp: Three Cases in Immunocompetent Children and Literature Review

Pyomyositis (PM) is an uncommon primary skeletal muscle infection caused mainly by Staphylococcus aureus that is characterized by single or multiple intramuscular abscess formation. In our ward, between 2013 and 2015, three children (two females and one male) aged from 2 to 12 years were diagnosed and treated for PM. Patients’ medical records and imaging studies were examined retrospectively. All patients, otherwise healthy, complained of limp, fever, and severe lower limb pain. Skin scratch lesions were detected in two cases; one of them showed an edematous appearance of the affected area. Multifocal bilateral abscesses of gemini and gastrocnemius were detected in the youngest patient; right obturator and iliac muscles were affected in the second patient; and right gluteus and pyriform muscles were involved in the third patient. All patients showed elevated acute phase reactants and had normal serum creatinine kinase levels. Blood cultures and polymerase chain reaction (PCR) investigations were negative in all cases. Magnetic resonance imaging (MRI) findings included muscle enlargement, deep fascia, high signal in subcutaneous tissues, and postgadolinium abscess formation. No patient required surgical or percutaneous drainage. All three were treated conservatively with intravenous oxacillin, associated with ceftriaxone in the first patient and ceftazidime in the other two, followed by oral antibiotic therapy for a period ranging from 5 to 6 weeks. Pyomyositis must be considered as an unusual cause of limp in children of all ages. When promptly diagnosed and adequately treated, it has a favorable outcome without relapses or sequelae as occurred in all our patients.