A 38-year-old Caucasian male was admitted because of neutropenic fever and sudden onset pain in his proximal right upper leg. Relevant medical history included haemophilia A, HIV infection and a relapsed primary central nervous system lymphoma. Physical examination showed a mild swelling of the right upper leg with palpatory pain at the lateral side and secondary functional limitation of movement. Laboratory analysis revealed highly elevated inflammation levels (CRP 247 mg/l) in the presence of deep neutropenia (90/mm3). Creatine kinase (CK) levels were not increased.
Plain radiography of the right hip and upper leg showed normal findings.
Doppler ultrasound imaging showed a normal aspect of the gluteus tendons without signs of tendinopathy. There was no hydrops in the hip joint, no swelling of the trochanteric bursa, and no apparent signs of bleeding, phlebitis or phlebothrombosis. (fig 1)
Multidetector CT before and after intravenous contrast excluded an active arterial bleeding in this haemophilia A patient. There was fluid between the muscle bellies of the quadriceps femoris muscle (mainly between the vastus lateralis - medialis - intermedius), as well as signs of subcutaneous fluid. (fig 2)
Magnetic resonance imaging (MRI) before and after intravenous contrast confirmed an extensive amount of fluid in the quadriceps muscle of the right leg with a small proximally located abscess (3.5/1 cm). There was extensive oedema in the entire vastus lateralis and intermedius muscles, extending to the distal musculotendinous junction and to the upper edge of the suprapatellar recess with moderate hydrops of the knee and involvement of the synovium. (fig 3)
Background
Primary pyomyositis is an infection of skeletal muscle occurring after a transient bacteremia without any contagious foci from the adjacent skin, soft tissue, or bone. Although originally regarded as an infection of tropic regions, it has been recognized in temperate climates with increasing frequency, especially in immunocompromised patients. The disease occurs most often in the lower extremities, but any muscle group can be involved. As striated muscles are generally resistant to infection, the exact pathogenesis of pyomyositis is still not fully understood. Risk factors include immunodeficiency, trauma, injection drug use, concurrent infection, and malnutrition. [1-3] Although Staphylococcus aureus is the most common causative pathogen of pyomyositis, Escherichia coli pyomyositis is emerging among patients with a hematologic malignancy, as it was in this case. [4]
Clinical perspective
Pyomyositis is often missed in the initial differential diagnosis because of its rarity, the often vague clinical presentation, and unspecific blood results. This delay in diagnosis can result in increased morbidity and mortality. [5] Three progressive stages of pyomyositis have been described: a diffuse inflammation (stage 1), leading to a suppurative stage with focal abscess formation (stage 2) and ultimately to systemic toxicity (stage 3). [6]
Imaging perspective
MRI is the optimal imaging modality as it is highly sensitive for muscle inflammation, even prior to the formation of abscess formation, and can demonstrate the extent of involvement. TypicaI findings include diffuse muscle enlargement with an increase in signal intensity on T2-weighted images, as well as single or multiple intramuscular abscesses with peripheral enhancement. [7,8] Although not as sensitive as MRI, computed tomography can be used for quickly identifying muscle swelling and well-delineated areas of fluid attenuation that display rim enhancement with contrast, as well as for radiographic-guided drainage of purulent material. [9] Ultrasonography can be a helpful tool during the purulent stage of infection in which diffuse muscle hyperechogenicity with localized hypoechogenicity and diffuse hyperemia may be seen. [10]
Outcome
Although stage 1 pyomyositis can be treated with antibiotics alone, most patients require both antibiotics and drainage for definitive management. For immunocompetent individuals, initial empiric parenteral antibiotic therapy should be directed against staphylococci, including methicillin-resistant S. aureus (MRSA) and beta-hemolytic streptococci. [7] For immunocompromised individuals, broad antibiotic coverage for gram-positive, gram-negative, and anaerobic organisms should be administered. The length of initial intravenous antibiotic therapy is generally 3 to 4 weeks but can vary considerably depending on the immune status of the host, the clinical course, and the number of abscesses. [2]
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Primary pyomyositis
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Based on the provided ultrasound, CT, and MRI images, the following key features are observed:
Considering the patient’s history of immunodeficiency (HIV, Hemophilia A, malignancy), current profound neutropenia, high fever, distal right thigh pain and swelling, and imaging findings suggestive of a muscular abscess, the most likely diagnosis is:
Pyomyositis, with a high suspicion of Gram-negative bacteria (e.g., Escherichia coli) infection.
Further confirmation can be obtained through abscess aspiration and culture or blood culture for pathogen identification.
Because the patient is currently in the acute infection phase and is immunocompromised, rehabilitation exercises must follow the principle of “gradual progression and individualization”:
Disclaimer: The above report is a reference analysis based on the available information and does not replace an in-person consultation or professional medical opinion. If you have any questions or if your condition changes, please consult a specialist promptly.
Primary pyomyositis
