Pyomyositis involves the formation of abscesses in striated muscle, and the usual signs of infection such as fever typically accompany it. The specific causes of pyomyositis vary by patient. In trauma-related cases, the trauma is believed to have rendered the muscle vulnerable to the subsequent infection. Streptococci and gram-negative bacilli also have been implicated. The condition affects primarily the large muscles including the hamstrings, quadriceps, gluteal group, and back, though a small number of patients experienced involvement of smaller muscles located in the upper extremities.
Patients usually seek medical care during the second stage.
Certain pathologic phenomena also predominate. Leukocytosis may or may not be present. The condition is sometimes misdiagnosed as osteochondritis, thrombophlebitis, or various sarcomas. One or more courses of such antibiotics as nafcillin, cephalexin, vancomycin, cefotaxime, oxacillin, and gentamicin given over several weeks invariably are needed to eliminate the causative infection. However, such protocols may not be sufficient to resolve widespread or well-established infections.