Objective: The objective of this study was to investigate the clinical and laboratory features of acute benign myositis associated with influenza A virus infection in children.

Methods: A retrospective analysis was performed on the clinical data of 118 children with acute benign myositis associated with influenza A virus infection who were admitted to the Children´s Hospital of Chongqing Medical University during the epidemic period of influenza A from February 2023 to May 2023.

Results: (1) Most of the 118 children were preschool- or school-age. The most common symptom was sudden lower limb pain after fever, and bilateral calf myalgia was more common. The muscle enzyme spectrum ranged from 187.21 to 32191.00 μg/L (median: 3053 μg/L). Creatine kinase isoenzymes ranged from 5.15 to 749.7 μg/L (median 41.82 μg/L). Myoglobin ranged from 102.79 to 1200 μg/L (median 674.9 μg/L). (3) Examination: electromyography, muscle color Doppler ultrasound, radiograph and cardiac color Doppler ultrasound in Benign acute childhood myositis in children were rarely positive. (4) Treatment and prognosis: besides bed rest and a reduction of physical activity, oseltamivir treatment, drugs to improve energy metabolism, fluid replacement and alkalinization of symptomatic treatment. All children had a good prognosis without sequelae.

Conclusions: This study summarized and analyzed the clinical characteristics of acute benign myositis associated with influenza A infection in children with the aim of allowing rapid and early diagnosis of the disease and reducing unnecessary diagnostic tests and treatments. Closely monitoring myalgia and the muscle enzyme spectrum is recommended to exclude other neuromuscular and metabolic diseases.