Pyomyositis Caused by Streptococcus agalactiae: A Case Report and Review of the Literature

Pyomyositis is a subacute bacterial infection of the skeletal muscle that is more common in the tropics. Staphylococcus aureus is the most common pathogen involved in pyomyositis, but Streptococcus agalactiae (group B Streptococcus (GBS)) can cause pyomyositis. We herein present a case of pyomyositis of the right gluteus maximus caused by GBS bacteremia (primary bacteremia). An 81-year-old man with a history of diabetes mellitus presented with warmth and painful swelling of the right lateral buttock. Computed tomographic (CT) images revealed swelling of the right gluteus maximus without an abscess, but soft tissue inflammation was apparent. The exploratory incision findings excluded necrotizing soft tissue infection. On day 2, two sets of blood cultures taken on admission grew Streptococcus agalactiae alone. Thus, pyomyositis caused by GBS was diagnosed. The patient received intravenous ampicillin therapy for two weeks. However, CT images revealed a new area of fluid accumulation in the right gluteus maximus, and no pus was aspirated during ultrasound-guided puncture. Following an additional week of intravenous ampicillin and four weeks of oral amoxicillin, the lesions resolved without surgical debridement. The present case is unique in that the patient developed pyomyositis due to GBS. We summarize and discuss seven cases of GBS pyomyositis, including our case, that have been reported to date.