Benign acute childhood myositis: a scoping review of clinical presentation and viral etiology.

Benign acute childhood myositis is a benign phenomenon often associated with influenza in children. The aim of this scoping review was to analyze the typical clinical picture and characteristics of benign acute childhood myositis patients. Furthermore, we aimed to analyze the epidemiology and viral findings. We performed a systematic scoping review. We searched PubMed, Scopus, Web of Science, and CINAHL databases in August 2023. We included observational studies that focused on children and reported at least 10 children. Our main outcome was to describe the typical clinical picture of benign acute childhood myositis patients. Furthermore, we aimed to report the typical laboratory findings and virus findings. A total of 211 studies were screened, and 22 studies were included in this review. The included studies were mainly from Europe (13 studies) and Asia (5 studies). Two studies were prospective, and the rest were retrospective. The mean age of the patients was 6.8 (CI 5.8-7.8) years. Benign acute childhood myositis appeared to be more prevalent among boys in all studies. The most prevalent symptoms were bilateral leg pain (pooled prevalence 92%), followed by fever (80%) and inability to walk (56%). Hospitalization rates varied between 4 and 100%, and the mean hospital stay was 3.6 (CI 3.3-3.9) days. Influenza B was the most common virus detected, followed by influenza A. Other reported viruses included herpes simplex, coxsackie-, enteroviruses, adeno-, respiratory syncytial, and parainfluenza viruses. All studies reported creatinine kinase levels, and the reported mean values varied between 100 and 4000 U/L, whereas only five studies reported C-reactive protein which was only slightly elevated.

Conclusion: According to a systematic assessment of published literature, benign acute childhood myositis patients were typically school-aged children, presenting with bilateral leg pain, fever, and inability to walk. Influenza A and B were the most reported viruses, but multiple other viruses have been associated with benign acute childhood myositis. These patients have high creatinine kinase values, but their hospital stay was rather short. Overall, this review provides important information for clinicians on the characteristic presentation of benign acute childhood myositis, and these findings may help to better identify these patients and reduce unnecessary tests.

What is known: • Benign acute childhood myositis has been mainly associated with influenza viruses, especially B influenza. • Typical patients have been reported to be under school-aged children, and boys have been reported to have a higher incidence.

What is new: • Many non-influenza viruses were also associated with benign acute childhood myositis, such as herpes simplex, coxsackie-, entero-, adeno-, respiratory syncytial, and parainfluenza viruses. • Typical symptoms are bilateral calf pain, fever, and inability to walk and creatine kinase levels were reposted to be increased.