Classic pyomyositis of the extremities as an unusual manifestation of Blastomyces dermatitidis: a report of two cases

Pyomyositis is an infection of skeletal muscle that, by definition, arises intramuscularly rather than secondarily from adjacent infection. It is usually associated with bacterial infection, particularly Staphylcococcus aureus. Fungi are rare causes, and Blastomyces dermatitidis has not been reported previously. In this case series, we report two cases of pyomyositis caused by B. dermatitidis. Cases were prospectively identified through routine clinical care at a single academic referral hospital. Two patients with complaints of muscle pain and subacute cough were treated at our hospital in 2007. Both patients were found to have pyomyositis caused by B. dermatitidis- in the quadriceps muscles in one patient, and in the calf muscle in another - by radiological imaging and fungal culture. Both were also diagnosed with pneumonia caused by B. dermatitidis (presumptive in one, confirmed in the other). There was no evidence of infection of adjacent structures, suggesting that the route of infection was likely direct haematogenous seeding of the muscle. A review of the literature confirmed that although B. dermatitidis has been described as causing axial muscle infection secondary to adjacent infection such as vertebral osteomyelitis, our description of isolated muscle involvement (classic pyomyositis) caused by B. dermatitidis, particularly of the extremity muscles, is unique. We conclude that B. dermatitidis is a potential cause of classic pyomyositis.