Pyomyositis caused by Streptococcus pneumoniae after allogeneic hematopoietic stem cell transplantation.

Pyomyositis is classified into two main types: tropical and non-tropical. Non-tropical pyomyositis occurs among various immunocompromised patients, and Staphylococcus aureus has been reported as the most common pathogen. Pyomyositis caused by Streptococcus pneumoniae is uncommon, and has not been previously reported after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Here, we report a unique case with pyomyositis caused by S. pneumoniae in the bilateral erector spinae muscles 34 months after allo-HSCT. The patient had an initial clinical response following the administration of intravenous benzylpenicillin potassium for 4 weeks. Although S. pneumoniae bacteremia is a rare bacterial infection after HSCT, the possibility of pyomyositis must be considered when a recipient develops S. pneumoniae bacteremia. Accurate diagnosis and the selection of appropriate antibiotics are necessary for the treatment of pyomyositis.