Benign Acute Childhood Myositis: Our Experience on Clinical Evaluation

Clinical Characteristics of 118 Pediatric Patients With Acute Benign Myositis Associated With Influenza A Virus Infection

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.

Benign acute children myositis: 5 years experience in a tertiary care pediatric hospital

Benign acute childhood myositis (BACM) is a self-limited childhood illness, and viral infections mainly cause it. Clinical and laboratory alterations usually normalize rapidly; generally, the only medical intervention required is supportive (hydration and analgesic medication). The low awareness about BACM often led to delayed diagnosis and unneeded ancillary investigations. This study aims to better characterize the clinical and laboratory features of BACM to improve the diagnostic process and inpatient and outpatient management. We conducted a retrospective study selecting all children admitted to Meyer's Children's Hospital-IRCCS (Florence, Italy) with a diagnosis of BACM over the last 5 years, both those visited at Emergency Department (ED) and those admitted to the Pediatric Unit. Clinical, laboratory, and instrumental data were collected from electronic clinical records and analyzed. Overall, sixty-five patients were enrolled; 49 children were visited and discharged directly from ED, whereas 16 were admitted in the Pediatric or Neurologic Wards. The median age was 6.56 years (IQR 4.9-9.1). Male gender (66.1%) and Caucasian ethnicity (70%) were prevalent. Most patients were admitted during winter, and a second peak was found in autumn. All patients had bilateral calf pain, most of them (87.7%) associated with asthenia and refuse to walk (93.8%). Prodromal symptoms were fever (75.3%), cough (32.3%), coryza (26.1%), sore throat (26.1%), and vomiting (15.3%). The median value of CPK was 1827 U/L (IQR 915.5-2462) at peak. CPK median time to normalization was 7 days (IQR 7-8.5) from the nadir. Influenza B was the virus most frequently BACM associated, followed by Influenza A; a novel association with Sars-CoV-2 has been detected. Two patients had pathogenic variants at the Next Generation Sequencing myopathies panel.    Conclusion: School-aged children admitted to the hospital with walking difficulty and myalgia, generally after an upper respiratory tract infection with a moderate CPK elevation, should remind at first of BACM. Rapid complaint resolution and biochemical markers normalization will prevent unnecessary tests and inappropriate therapies. What is Known: • BACM is a self-limited syndrome associated with acute infections. Influenza A and B viruses are the main etiological agents, but BACM may be related to many other microorganisms like Parainfluenza virus, Epstein-Barr virus, Cytomegalovirus, Human herpesvirus 6, Respiratory syncytial virus, Coxsackieviruses, Mycoplasma pneumoniae, Streptococcus pyogenes, Legionella, and Salmonella spp. • Clinical and laboratory alterations usually normalize rapidly; generally, the only medical intervention required is supportive (hydration, analgesic medication). Evolution in rhabdomyolysis and kidney damage is possible but rarely reported. What is New: • Sars-CoV-2 could be an emerging possible cause of BACM. During and after the Sars-CoV-2 outbreak, virus infection seasonality has changed, and so has BACM seasonality. • Screening tests for muscular and metabolic disorders are recommended in recurrent myositis and/or cases with marked CPK elevation (≥ 5000 U/L).