Characteristics of Patients with Benign Acute Childhood Myositis (BACM)

Background: Benign acute childhood myositis (BACM) is a rare complication of viral URTIs, usually occurring in winter. It is characterized by acute onset of bilateral calf pain and difficulty/refusal to walk. A prodromal phase precedes these manifestations, consisting of catarrhal and constitutional symptoms. These are associated with increased muscle-specific enzymes, usually normal inflammatory parameters, and leukopenia. Objective: Our study aimed to define the demographic, clinical, and laboratory characteristics of BACM patients and determine the etiology leading to their development. Methods: Medical charts for patients diagnosed with BACM from October to April 2023/2024 at the Pediatric Clinic Clinical Center University of Sarajevo, Department of Allergology, Rheumatology, and Immunology were reviewed retrospectively. Relevant medical information was collected for 20 patients. Statistical analysis was done in Microsoft Excel 2013. Results: Demographic analysis demonstrated male predominance (75%), with primarily school-aged children affected (median age 8.36). Most cases occurred in winter (60%). The majority of patients presented with bilateral calf pain (100%), difficulty walking (90%), and fever (100%). All cases demonstrated increased CK levels, with median values of 3779 U/L; a notable number had leukopenia (70%). The most commonly isolated pathogen was Influenza B virus (75%). Conclusion: BACM is relatively rare but presents acutely and leads to plenty of distress for both patients and their parents. A child with coryzal symptoms complicated by bilateral calf pain or difficulty/refusal to walk and an increase in CK levels should raise suspicion of BACM. The condition is self-limiting and usually resolves without complications.