❚ Laboratory evaluation will often show mild neutropenia, thrombocytopenia, and mild elevation in CK.7,8 CRP is typically normal.4,7,9 In a retrospective study of 28 admissions for BACM from 2001 to 2012, common findings included leukopenia (35%), neutropenia (25%), and thrombocytopenia (21%). The median CK value was 4181 U/L.4 In another analysis of BACM cases, mean CK was 1872 U/L.5
❚ Biopsy is unnecessary; however, calf muscle samples from 11 of 12 children with suspected BACM due to influenza B infection were consistent with patchy necrosis without significant myositis.10
❚ Complications. Rhabdomyolysis, although rare, has been reported with BACM. In 1 analysis, 10 of 316 patients with influenza-associated myositis developed rhabdomyolysis; 8 experienced renal failure. Rhabdomyolysis was 4 times more likely to occur in girls, and 86% of cases were associated with influenza A.6 Common manifestations of rhabdomyolysis associated with influenza include diffuse myopathy, gross hematuria, and myoglobinuria.6
❚ Treatment is mainly supportive.4,8,9 Antivirals typically are not indicated, as the bilateral calf pain manifests during the recovery phase of the illness.4,9,11 BACM is self-limited and should resolve within 3 days of myositis manifestation.2 Patients should follow up in 2 to 3 weeks to verify symptom resolution.2
If muscle pain, swelling, and tenderness worsen, further work-up is indicated. In more severe cases, including those involving renal failure, intensive care management and even dialysis may be necessary.4,6
❚ Our patient was hospitalized due to fever in the setting of neutropenia. Ultimately, he was treated with acetaminophen and intravenous fluids for mild dehydration and elevated CK levels. He was discharged home after 3 days, at which time he had complete resolution of pain and was able to resume normal activities.
The Takeaway
Benign acute childhood myositis is a self-limited disorder with an excellent prognosis. It has a typical presentation and therefore should be a clinical diagnosis; however, investigative studies may be warranted to rule out more ominous causes. Reassurance to family that the condition should self-resolve in a few days is important. Close follow-up should be scheduled to ensure resolution of symptoms.
CORRESPONDENCE
Nicholas A. Rathjen, DO, William Beaumont Army Medical Center, Department of Soldier and Family Care, 11335 SSG Sims Street, Fort Bliss, TX 79918; nicholas.a.rathjen@gmail. com