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Pyomyositis is an acute infectious disorder affecting the skeletal muscle. Although seen more commonly in the tropics, cases are being reported in temperate countries, including the United States. We report a case of nontropical pyomyositis in a 58-year-old diabetic man who presented with a vague chest wall swelling. His initial clinical presentation and imaging findings suggested an intramuscular hematoma. He later developed fever with increased swelling, and pyomyositis was diagnosed after an aspiration of the swelling yielded Streptococcus agalactiae. Aspiration of the abscess and the use of appropriate antibiotics led to complete resolution of the disease. We discuss possible factors in diabetics that might predispose them to pyomyositis.
Pyomyositis is a primary suppurative infection of the skeletal muscle occurring in the absence of adjacent bone, soft tissue, and skin involvement. This entity was first described as an endemic disease of the tropics by Scriba in 1885 (1). Since then, many reports have emerged in temperate climates, with the first case in the US described in 1971 (2). We present the case of a 58-year-old man with a history of Hodgkin's lymphoma and diabetes who developed an acute swelling of the chest wall that was ultimately diagnosed as pyomyositis.
A 58-year-old man presented with a painful swelling of the right chest wall of 1 week duration. He denied fever, chills, night sweats, or recent trauma to that area and had no cough or dyspnea. His pain radiated from his chest to the right axilla and shoulder and increased with active movement of his arm. At the age of 51, the patient was diagnosed with Hodgkin's lymphoma, with extensive lymphadenopathy in the right inguinal area extending to the right iliac vein. He completed chemotherapy and radiation therapy to the right inguinal and pelvic areas and had been in remission for the past 5 years. A computed tomography (CT) scan of the chest, abdomen, and pelvis done 1 week prior to admission as part of surveillance was normal. His vital signs were within normal limits. He had a poorly defined 8 × 8 cm tender erythematous mass involving his right chest wall with a soft consistency. The mass centered around an old surgical scar from a port-a-cath that was removed a year earlier. There were no enlarged lymph nodes. Lungs were clear to auscultation, and the rest of the physical examination was within normal limits. The white blood cell count was 16.8 × 109/L with a left shift and 82% neutrophils. A random blood sugar was 310 mg/dL, and the hemoglobin A1c level was 10.4%. Blood cultures were negative. An ultrasound revealed a diffuse soft tissue swelling with no evidence of an abscess. A CT of the chest with contrast demonstrated a nonspecific fluid loculation measuring 5.0 × 2.8 cm between the right pectoralis major and minor muscle (Figure). On day 3, the patient spiked a temperature of 100.5°F with an increase in the size of the swelling. An ultrasound-guided incision and drainage was done, and 35 mL of thick pus was aspirated. The culture from the aspirate grew Streptococcus agalactiae. He was treated with 4 weeks of intravenous antibiotics resulting in good clinical improvement. There was no recurrence of symptoms on follow-up a month later.
Pyomyositis is an acute bacterial infection reported in young healthy children and adults residing in the tropics. The nontropical entity seen in temperate climates is more common in older patients and in those with immunocompromising diseases, such as HIV, diabetes mellitus, malignancies, autoimmune disorders, and chronic liver disease (3, 4). The pathogenesis of pyomyositis is poorly understood. Prior muscle injury and transient bacteremia probably contribute to its development (5). The fibronectin-binding receptors on muscle cells are possible pathways for bacterial entry (6). Muscles frequently involved are the large muscle groups, like the quadriceps, glutei, and trunk muscles (7). Staphylococcus aureus is the most common organism isolated (5, 7). The other rare causative organisms include Streptococcus groups B and C, gram-negative organisms including Escherichia coli and Klebsiella species, anaerobic bacteria, Mycobacterium species (M. avium complex and M. tuberculosis), and fungi (5, 6, 8). Pyomyositis is often misdiagnosed in its initial stages, as the clinical presentation is similar to muscle hematoma, cellulitis, osteomyelitis, and thrombophlebitis. The diagnosis is facilitated by radiologic techniques that can demonstrate the presence of fluid collections, and contrast magnetic resonance imaging is the preferred technique (9). Definitive treatment includes drainage of the abscess and long-term intravenous antibiotic therapy.
This patient developed pyomyositis at the site where he had a prior port placed for chemotherapy, which might represent an area of local muscle injury. His diabetes was uncontrolled with a hemoglobin A1c of 10.9%. In a review of 246 cases of pyomyositis in non–HIV infected patients, diabetes mellitus was the most common association seen (6). Diabetes mellitus may predispose a patient to muscle damage and various bacterial infections. Microangiopathic changes and large vessel atherosclerosis are associated with microinfarcts in the muscle (10). The subsequent decrease in blood supply and local hypoxia may increase the risk of infection and abscess formation. Markedly thickened basement membranes in capillaries have been noted in diabetics and may inhibit migration of neutrophils (11). Diabetic patients have defective neutrophilic function and defective T cell–mediated immune responses, which make them prone to infections (12–14).
This patient had pyomyositis secondary to Streptococcus agalactiae, which was isolated from his aspirate. S. agalactiae is known to cause infection in neonates and pregnant women, but rarely causes infection in adults. A PubMed search revealed only 2 cases of pyomyositis in diabetics caused by S. agalactiae (15, 16). The patient improved dramatically on 4 weeks of intravenous antibiotic therapy. Prolonged intravenous antibiotic therapy is recommended to avoid mortality and complications such as sepsis and toxic shock syndrome.