Key result
Influenza B childhood myositis presents with higher myoglobin and CK-MB than influenza A despite favorable outcomes.
Why the study?
Are there differences in severity, clinical course, and outcomes between influenza A- and B-associated benign acute childhood myositis?
Cohort (n=82)
Are there differences in severity, clinical course, and outcomes between influenza A- and B-associated benign acute childhood myositis?
Influenza-associated benign acute childhood myositis is a brief, self-limited condition with favorable outcomes, though influenza B may present with higher myoglobin and CK-MB levels.
Captured external expert commentary on this paper, strongest first. Original sources are linked where available.
“Influenza B is more common with viral myositis”
Supports expectant management for most influenza-associated BACM cases; leaves open need for prospective studies on A versus B differences.
BACKGROUND: To characterize the severity, clinical course, and 6-month outcomes of influenza-associated benign acute childhood myositis (BACM) during the 2024-2025 season and to explore differences between cases associated with influenza A and B. METHODS: We retrospectively analyzed 82 children who met the BACM diagnostic criteria and none of the exclusion criteria among 11,528 children with laboratory-confirmed influenza between October 2024 and March 2025. Clinical features, first-presentation laboratory findings and outcomes were compared between influenza A- and B-associated cases. Venous measurements were based on the first sample obtained during evaluation for leg pain or gait disturbance. RESULTS: The 82 patients (mean age, 6.8 ± 2.1 years; range, 3-14 years) included 55 boys, 27 influenza A cases and 55 influenza B cases. Leg pain or gait disturbance developed 1-9 days after influenza symptom onset and resolved within 3-5 days. None required intensive care or renal replacement therapy; first-presentation urinalysis and serum creatinine were normal in all patients. Influenza B-associated cases had higher myoglobin, more frequently had creatine kinase (CK)-MB ≥50 U/L, and had lower white blood cell and platelet counts. At 6 months, caregivers reported no recurrence, readmission or persistent muscular or neurologic symptoms. CONCLUSIONS: Influenza-associated BACM was brief and self-limited, with favorable 6-month outcomes. Influenza B-associated cases had higher myoglobin and more often had CK-MB ≥50 U/L, but these exploratory findings do not establish greater severity or myocardial injury. Management should be individualized; cardiac troponin I and echocardiography may help contextualize CK-MB elevation when myocardial involvement is suspected.
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Du et al. (2026) conducted a cohort in Influenza-associated benign acute childhood myositis (n=82). Influenza B vs. Influenza A was evaluated on Clinical features, laboratory findings, and 6-month outcomes. Influenza B-associated benign acute childhood myositis presented with higher myoglobin and more frequent CK-MB ≥50 U/L than influenza A, though all cases had favorable 6-month outcomes.
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