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You are seeing a 4-year-old boy right now (February 2025) with 4 days of fever, sore throat, cough, congestion, headaches and decreased appetite who has now developed refusal to walk. He complains of bilateral calf pain. When he tries to walk, he does so on his tip-toes, and prefers to hold his ankles in a plantar-flexed position. His entire family is sick with similar symptoms but without the leg pains and walking issues.
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February 12, 2025 at 12:08 pm
B) Viral muscle inflammation
Many viruses but particularly influenza, especially influenza B, can cause a benign childhood myositis. Currently in February 2025 the U.S. is experiencing a massive influenza outbreak. A large European scoping review found the mean age to be 6.8 years, a higher prevalence in boys than girls, and the vast majority with bilateral symptoms. Mean CK levels varied between 1,185 to 14,319 in the included studies. There is a very small risk of rhabdomyolysis (~3% in one study) and labs to assess kidney function and myoglobinuria should be performed. Treatment includes NSAIDs for pain and hydration to prevent kidney injury, and most children recovered in 4-5 days. Outpatient management is often possible but there are no clear guidelines for when to admit for IV hydration. Suggested CK level cutoffs for inpatient admission and management range from 3,000 (Pediatric EM Morsels) to 10,000 (ChatGPT). Patient symptomatology, hydration, ability to follow up, and specific lab abnormalities all factor into the decision. Regardless, patients should have repeated CK levels until they are noted to be falling and pain is improving.