Pneumococcal Pyomyositis: A Rare, But Growing Concern

Pneumococcal pyomyositis is a rare bacterial infection of striated muscle, but 2 recent cases have put it on the radar of infectious disease specialists.

Pyomyositis—bacterial infection of striated muscle, usually accompanied by abscess—is a rare infection, which is why 2 recent cases are such big news. Before 1970 it was reported most often in tropical climates. In the last 40 years, clinicians have begun to report sporadic cases in more temperate climates. They seem to occur most often in patients diagnosed with diabetes or autoimmune disease or who inject drugs. Staphylococcus aureus and Streptococcus pyogenes are the most common causative agents. Rarely, gram-negative organisms or fungi have been implicated and, from time to time, microbiologists have identified Streptococcus pneumoniae as the cause.

Now, clinicians in Minnesota have identified 2 cases of pneumococcal pyomyositis. The first was found in the shoulder of a 47-year-old African American man with stage IV Hodgkin’s lymphoma who had been vaccinated 18 months earlier with pneumococcal polysaccharide vaccine. He was successfully treated with antibiotics. The second case occurred in the knee of a 52-year-old homeless man with paranoid schizophrenia. The second patient was also treated successfully, but lost to follow-up when he failed to appear for subsequent appointments.

In an article published online on April 20, 2012, in Clinical Infectious Diseases, researchers at the University of Minnesota reported on the 2 new cases and reviewed previous cases of pneumococcal pyomyositis in adults and children. They found 35 reports in the last 40 years, of which 24 cases occurred in at-risk individuals, with the others in apparently normal individuals.

After finding that two-thirds of these patients had a previous respiratory or meningeal pneumococcal infection, the researchers concluded that pyomyositis probably results from secondary seeding to muscle. They also found that, compared to normal individuals, at-risk individuals tended to have prolonged intervals between symptomatic muscle infection and pyomyositis diagnosis—and a more indolent course; significantly higher risk of disseminated disease in multiple non-contiguous muscles or comorbid meningitis; and more complications.

Only 1 of the 35 patients died. All others were treated successfully with antibiotics and surgical drainage.

Ms. Wick is a visiting professor at the University of Connecticut School of Pharmacy and a freelance writer from Virginia.