Pyomyositis is characterized by a purulent bacterial infection of skeletal muscles and occurs most frequently in tropical regions. However, pyomyositis has also been reported in temperate climates in association with other diseases such as diabetes mellitus. Pyomyositis is usually caused by a Staphylococcus aureus infection and can be secondary to a mechanical trauma. Early manifestations are often too mild and diffuse for a concise diagnosis, which can only be ascertained by means of imaging techniques, muscle biopsy, and bacterial cultures.
Provided a timely and correct diagnosis, pyomyositis can be efficiently managed with appropriate antibiotics and surgical debridement. Untreated pyomyositis can be fatal because of septic complications.
Pyomyositis, also referred to as myositis tropicans, typically manifests as an inflammatory suppuration in skeletal muscles because of bacterial infection of the muscle tissue . Pyomyositis occurs more often in the tropical climate. Patients from temperate regions are scarce and typically develop pyomyositis because of an ongoing immunosuppressive therapy, a proven diabetes mellitus background, or due to HIV infection . In most cases, Staphylococcus aureus is the causative infectious agent. Streptococci from groups A, B, C, and G as well as pneumococci, Gram-negative bacilli, and Haemophilus bacteria have been reported in rare cases . Bacterial infection can occur after a mechanical trauma such as a fall or a traffic accident  .
Pyomyositis symptoms develop slowly. Patients often suffer from diffuse and unspecific early manifestations like fever, myalgia, swelling, and tenderness. Later on, redness of the skin area and increased warmth of the skin above the affected muscle may occur. Reports have indicated that quadriceps, biceps, iliopsoas, gastrocnemius, pectoralis major, serratus anterior, abdominal, gluteal, and spinal muscles are more prone to be affected by pyomyositis  . Pyomyositis can affect both genders and all age groups, however, an increased incidence has been reported in males (overall male to female ratio - 1.5: 1), particularly in young males . The death can occur if the infection is untreated .
The first suspicion of pyomyositis can be formulated on the basis of the patient's history. If the patient has recently traveled to tropical countries, has been involved in a traffic accident, or is being treated with immunosuppressive agents, further investigations are indicated to validate the suspicion. Blood laboratory tests are typically too unspecific but may be used for cross-checking purposes. Elevated white blood cell counts, particularly peripheral blood eosinophils, together with normal serum creatine kinase (CK) are often found in pyomyositis patients  . Blood cultures can reveal a bacterial infection .
The gold standard for a final diagnosis is provided by computed tomography (CT) or magnetic resonance imaging (MRI), which can pinpoint the exact locations of the suppurative inflammation in the affected muscles . A muscle biopsy may also be ordered to prove edema in early pyomyositis or necrotic degenerations with abundant inflammatory cells in advanced pyomyositis  . Pus aspiration and analysis will help identify the causative bacteria and guide further management and treatment. In the minority of cases, the analyzed pus can be sterile .