Pyomyositis a challenging diagnosis in nontropical countries

Diagnosis of pyomyositis, a bacterial muscle infection, among hospitalized children and adolescents with musculoskeletal pain remains difficult for many clinicians and requires greater awareness, according to a recent study. 

“In contrast to tropical regions, it is rarely recognized in temperate countries, but incidence is increasing and major studies are missing,” the investigators said. 

Patients aged <18 years hospitalized with pyomyositis in 11 Swiss children’s hospitals between January 2010 and December 2022 were included in this retrospective multicentre study. The investigators identified patients using the ICD-10 code (Myositis; M60–M60.9) and extracted data from electronic hospital records. 

Of the 331 patients (aged 2–17 years, median 8 years) identified, 102 met the case definition for pyomyositis. Most of them showed no underlying illness, and all experienced fever and localized pain. [Pediatr Infec Dis J 2024;43:831-840] 

In addition, 100 patients (98 percent) suffered from impaired movement and 39 (38 percent) had local swelling. The most affected muscles were the pelvic (57 percent) and leg (28 percent). 

Blood or tissue cultures were also obtained in 94 (92 percent) and 59 (57 percent) patients, respectively. Positive results were found in 55 (58 percent) blood and 52 (88 percent) tissue cultures, with S. aureus (35 and 19, respectively) and S. pyogenes (12 and 15, respectively) as the predominant causative agents. 

During hospitalization, all patients received antibiotic therapy for a median of 10 days. This was followed by outpatient treatment for a median of 16 days in 95 (93 percent) participants. Surgery was also performed in 59 (57 percent) patients. 

Previous studies reported favourable outcomes in patients with early diagnosis and prompt antibiotic treatment, resulting in complications-free recovery. Assigning infection severity (stage 1–3) also improved treatment strategies. [J Pediatr Orthop 2021;41:e849-e854; J Neurol Sci 2020;413:116767] 

Rising cases 

“Similar to other studies, we observed an increase in pyomyositis cases over the time period, but this was not linked to the emergence of resistant bacterial infections such as community-acquired methicillin-resistant S. aureus infections in the US,” the researchers said. [Pediatr Infect Dis J 2015;34:1-4; Clin Infect Dis 2006;43:953-960; J Bone Joint Surg Am 2002;84:2277-2286] 

“It is possible that the increase is due to improved diagnostic procedures, specifically the broader use of MRI, and greater awareness among healthcare professionals,” they added. 

Other potential contributors to the disease include changes in environmental and lifestyle factors and global warming. Incidence of pyomyositis, once deemed a tropical disease, is becoming more prevalent in many temperate countries. [Pediatr Infect Dis J 2021;40:e276-e278; Int Orthop 2010;34:109-113] 

Furthermore, “[w]e did not observe seasonal differences as described for rainy seasons in tropical countries, which is attributed to the facilitated bacterial skin colonization in humid environments,” the investigators said. [Curr Infect Dis Rep 2016;18:12; Int Orthop 2018;42:1143-1147; J Trop Pediatr 2013;59:243-245; Rev Infect Dis 1991;13:339]