Thigh pyomyositis caused by group A streptococcus in an immunocompetent adult without any cause

Pyomyositis is typically caused by Staphylococcus aureus, and is rare in temperate climates, although its prevalence has been recently increasing. This infection often involves the thigh, and is associated with immunodeficiency. We report the case of a healthy 20-year-old Japanese woman who experienced a fever and continuous pain for several days. She was admitted to our hospital and was diagnosed with pyomyositis after we discovered an abscess between the muscles of her dorsal distal left thigh using computed tomography. This is a rare case of thigh pyomyositis, as it was caused by group A streptococcus and occurred in an immunocompetent adult from a temperate climate. Our review of the literature revealed that group A streptococcus pyomyositis typically occurs in temperate climates, among young adults without any underlying disease, and is associated with a poorer prognosis, compared to general pyomyositis. We suggest that pyomyositis should be considered when immunocompetent adults present with apparently idiopathic inflammatory muscle lesions.


Background
Pyomyositis is a bacterial infection of the skeletal muscle that is most commonly caused by Staphylococcus aureus (S. aureus; 90% of tropical cases and 75% of temperate cases) [1], although it is relatively rare in temperate climates. Another 1-5% of cases involve group A streptococcus, and other rare cases may involve streptococcus (groups B, C, and G), pneumococcus, Neisseria spp., Haemophilus spp., Aeromonas spp., Serratia spp., Yersinia spp., Pseudomonas spp., Klebsiella spp., and Escherichia spp. [1]. The development of pyomyositis is typically associated with immune-related conditions (e.g., diabetes mellitus, the use of corticosteroids, human immunodeficiency virus (HIV) infection, acquired immune deficiency syndrome (AIDS), and malignancies), and most commonly affects the muscles of the lower extremities (i.e., the thighs and calves) [2]. Among immunocompetent patients, pyomyositis is typically accompanied by a history of a traffic accident [3] or vigorous exercise [4]. Furthermore, pyomyositis caused by group A streptococcus (GAS) is a known complication of chicken pox among children [5]. Therefore, we report a case of apparently idiopathic thigh pyomyositis that was caused by GAS in an immunocompetent adult.

Case presentation
A 20-year-old Japanese woman was working in a restaurant and experienced discomfort in her left thigh on the seventh day before her hospital admission. On the next day, she felt pain in the same area while walking, and subsequently consulted a physician, who prescribed an antiphlogistic sedative patch on the fifth day before her admission. On the third day before her admission, she Open Access BMC Research Notes *Correspondence: smile.kenzaka@jichi.ac.jp 3 Division of Community Medicine and Career Development, Kobe University Graduate School of Medicine, 2-1-5 Arata-cho, Hyogo-ku, Kobe, Hyogo 652-0032, Japan Full list of author information is available at the end of the article developed a fever (38 °C) and subsequently consulted another physician, who prescribed an antipyretic drug. However, she continued to experience fever and pain in her left thigh flexor during rest. Therefore, she consulted another physician and was admitted to our hospital, where she was prescribed a single dose of acetaminophen (400 mg). She did not have a history of domestic or overseas travel, participation in outdoor activities, or trauma. Upon admission, she had a blood pressure of 110/63 mmHg, a pulse of 107 beats/min, a respiratory rate of 16 breaths/min, and a temperature of 38.9 °C. Her left thigh flexor appeared slightly red, with mild swelling, warmth, and pain. However, her head, lungs, heart, abdomen, and back did not exhibit redness or swelling. Her white blood cell count was 12,100 cells/mm 3 , her hemoglobin level was 10.8 g/dL, and her C-reactive protein level was 24.11 mg/dL. Her liver and renal functions were normal, and the HIV antibody/p24 antigen test (fourth generation) provided negative results. However, enhanced computed tomography (CT) revealed fluid between the dorsal distal muscles of her left thigh and an enhanced margin of fluid ( Fig. 1), which we diagnosed as an abscess. There were no other abscess-like formations outside of her lower extremities.
An incision was made in her left thigh on the day of admission, the abscess was continuously drained, and we treated her using ampicillin/sulbactam (four doses per day, up to 12 g daily). Two sets of blood cultures provided negative results; however, a culture of a fasciotomy specimen from the abscess revealed positive results for GAS. Definitive identification of the GAS isolate was performed using the rapid streptococcus test (Rapid ID32 STREP; bioMerieux SA, Marcy l'Etoile, France). Therefore, we changed the patient's treatment to penicillin G (24 million units per day via continuous infusion) on day 5. However, drug eruption in response to the penicillin G was suspected on day 12, and we changed the antibiotic to clindamycin on day 13 (2700 mg in three doses per day). We stopped the continuous drainage on day 15, and switched the treatment to oral clindamycin on day 16 (600 mg three times per day). The patient was discharged after 17 days in the hospital, and her antibiotic treatment lasted 4 weeks. We did not observe any side effects that were related to the clindamycin treatment. The patient has remained in good health during the 1-year follow-up after her discharge from the hospital.

Conclusions
We encountered a rare and apparently idiopathic case of non-tropical pyomyositis that was caused by GAS in a healthy young Japanese woman. In this context, pyomyositis is rare in temperate climates, although it has recently become more frequent in these climates [6]. The clinical features of temperate and tropical cases of pyomyositis are summarized in Table 1.
It is difficult to diagnose pyomyositis, as there are no specific symptoms, and the only early symptoms are minor pain and swelling. Therefore, patients are often slow to consult with a physician, and the diagnosis is often delayed by 2-3 weeks [1]. When the diagnosis is delayed, death can be caused by septic complications, which include toxic shock syndrome [9]. In the present case, the patient exhibited minor swelling, redness, and warmth in her thigh, and we were able to rapidly diagnose pyomyositis based on our physical findings and the CT results. This rapid diagnosis allowed us to quickly start antibiotic treatment and drainage, which are both critical for treating pyomyositis (except during the early stage) [30].
We reported a rare case of apparently idiopathic thigh pyomyositis that was caused by GAS in an immunocompetent adult. Furthermore, our review of the literature revealed that GAS pyomyositis typically occurs in temperate climates, among young adults without any underlying disease, and is associated with a poorer prognosis, compared to general pyomyositis. Therefore, pyomyositis should be considered when a patient presents with inflammatory lesions in the thigh or other common Mortality [6,9] (%) 6.0-9.4 0.5-2.0