Case Presentation: A 42-year-old man presented to an outside hospital emergency department with a complaint of worsening left hip pain and swelling. He attributed the pain to a sports related injury from a baseball tournament he had participated in the prior week. He was diagnosed with muscle strain on two previous emergency department visits. Additional injuries included a left third digit crush injury and right shin abrasion. The patient had a history of well controlled human immunodeficiency virus (HIV) on anti-retroviral therapy with a CD4 count of 396. He had no history of opportunistic infections and denied intravenous drug abuse. He was tachycardic, tachypneic, with a leukocytosis. Blood cultures were obtained. MRI of the left hip suggested necrotizing fasciitis. He was started on broad spectrum antibiotics and transferred to our hospital where he continued to be tachycardic, tachypneic, febrile, with leukocytosis, up to 30,000 mm3. The left hip was erythematous, tender to palpation, with decreased range of motion. The right shoulder was also found to be swollen, tender, with decreased range of motion. He then recalled that he had injured his right shoulder about two weeks earlier while lifting weights. Review of the outside imaging and exam were less concerning for necrotizing fasciitis. Further imaging revealed left gluteal and psoas abscesses. He underwent aspiration of his right shoulder and left hip as well as an open right shoulder incision and drainage, which revealed copious subdeltoid pus but no glenohumeral joint infection. The patient then underwent incision and drainage of his left gluteal and left psoas abscesses which also revealed involvement of the left hip joint. Blood cultures from both the outside hospital and our hospital, as well as surgical cultures grew methicillin-sensitive Staphylococcus aureus.
Discussion: Pyomyositis is an abscess of skeletal muscle thought to occur from a transient bacteremia in the setting of muscular injury. It has been increasing recognized in temperate climates in immunocompromised patients. Most immunocompromised patients with pyomyositis are HIV positive. The remainder may be on immunosuppressive drugs, have an underlying malignancy, or diabetes mellitus. Other predisposing factors include recent trauma, intravenous drug abuse, and ongoing infection. Methicllin-sensitive Staphylococcus aureus is the most common cause followed by methicillin-resistant Staphylococcus aureus. Patients usually present with fever and localized muscle pain, although more than one muscle can be involved. Three clinical stages have been described: the first with muscle pain, fever, leukocytosis but no discrete abscess; the second with abscess formation; and the third with bacteremia and metastatic abscesses. Other complications can include endocarditis, septic arthritis, and septic emboli.
Conclusions: Pyomyositis is usually seen in the tropics but has been occurring more in temperate climates especially with the emergence of HIV. As with our patient, pyomyositis can be misdiagnosed as muscle strain, cellulitis, septic arthritis, necrotizing fasciitis, or other forms of myositis. It is important for physicians who encounter the immunocompromised patient with localized muscle pain to consider pyomyositis as a potentially serious diagnosis.