A Multicenter Retrospective Study of Epidemiological Trends in Benign Acute Childhood Myositis Before and After the COVID-19 Pandemic

Background Benign acute childhood myositis (BACM) is a rare condition that usually follows viral infections, predominantly affecting school-aged males. At onset, patients typically complain of soreness in the lower limbs and bilateral calves, with gait abnormalities such as refusal to bear weight, a wide-based gait, or toe walking. This is a generally self-limiting condition, but it may require hospitalization for the initiation of intravenous hydration in severe cases. Renal involvement due to rhabdomyolysis is extremely rare. The diagnostic work-up is often limited by the lack of awareness among pediatricians. This study aimed to describe its epidemiological and clinical characteristics, summarizing cases before and after the COVID-19 pandemic, and providing suggestions for the management of this condition. Methods This retrospective multicenter study used data from the AULSS 7 Pedemontana database. We included consecutive patients with clinical and biochemical diagnosis of BACM who were admitted to the Emergency Departments of three Italian hospitals between January 1, 2012, and December 31, 2024. Patients were identified through an extensive search using discharge codes according to the International Classification of Diseases, 9th Revision, Clinical Modification. Statistical analyses were performed using IBM SPSS Statistics for Windows, Version 21 (Released 2013; IBM Corp., Armonk, New York, United States). Results A total of 55 episodes of childhood myositis affecting 51 patients were identified. Most patients exhibited fever, rhinitis, pharyngitis, asthenia, and hyporexia; a smaller proportion presented with gastrointestinal symptoms. Consistent with the current literature, the predominant symptom of myositis was lower limb pain (n = 49, 89%), followed by refusal to ambulate (n = 30, 55%), often characterized by a wide-based gait (n = 17, 31%), typically following febrile illness. The incidence apparently increased in the post-pandemic period, as did the mean creatine phosphokinase levels increase from admission (928 IU/L vs. 146 IU/L, p = 0.03). A slower normalization of creatine phosphokinase values was also observed during the post-pandemic period (8.5 days vs. 4.2 days, p = 0.004). A higher hospitalization rate was noted in the post-pandemic group (n = 21, 70%) compared to the pre-pandemic group (n = 12, 48%), although this difference did not reach statistical significance (p = 0.10). The need for hospitalization was directly associated with elevated creatine phosphokinase levels (p = 0.05), renal impairment (p = 0.05), elevated blood urea levels (p < 0.0001), older age (p = 0.04), and inversely correlated with the presence of gastrointestinal symptoms (p = 0.001). Conclusion While it remains benign, a standardized approach is needed for childhood myositis diagnosis and management, balancing the risks of unnecessary hospitalizations and potential complications. All patients should undergo blood tests along with a urine dipstick, electrocardiogram, and, if possible, influenza A/B swab testing. Patients with mild symptoms, low muscle enzyme levels, no renal impairment, and good family compliance may be discharged home with parental reassurance about the benign nature of the condition. Otherwise, we suggest hospitalization or short-term observation for intravenous hydration and laboratory monitoring. Further research is warranted to elucidate potential post-pandemic changes in disease presentation.