Benign Acute Childhood Myositis

Benign Acute Childhood MyositisPreviously, we have discussed the potential counterproductive effects of saying the phrase “It’s just a virus.” Aside from the perception that their child’s illness is “no big deal,” this phrase is also inaccurate as it implies that viral illness is not significant. Certainly, we know that viral infections can have significant negative affects on organs  (ie, Myocarditis, PericarditisMumps, Guillain-Barre Syndrome, Aplastic Anemia).  Fortunately, many times viral induced illness is self-limited and does resolve without long-term consequences to any organ systems. One such condition may initially make you worry about the kidneys (Rhabdomyolysis), but typically subsides without lasting injury. Let us take a minute to familiarize ourselves with Benign Acute Childhood Myositis:


Benign Acute Childhood Myositis: Basics

  • Exact incidence is not known (often referred to as various other names)
    • Influenza-associated myositis
    • Viral Myositis
    • Acute Myositis
  • Inflammatory process that leads to isolated skeletal muscle degeneration.
  • Transient and self-limited syndrome
  • Can be seen within an epidemic. [Mall, 2011]
  • Associated with viral infections:
    • Influenza B [Mall, 2011; Sonmez, 2004]
    • Influenza A
    • Enterovirus
    • Adenovirus
    • Parainfluenza
    • Nonspecific viral infections
    • Mycoplasma pneumoniae
  • Most commonly affects:
    • Children 6-8 years of age [Mall, 2011]
    • Boys more often than girls [Mall, 2011]
  • Typical course of the illness is benign without lasting consequences. [Rosenberg, 2016; Mall, 2011]
    • Largest series of cases found no manifestations of myoglobinuria or rhabdomyolysis.
      • When it does occur, it tends to occur more often in females.
      • Higher CPK levels should still warrant concern.
    • All of these cases recovered without residual weakness or pain.
    • Typically resolves within a week.


Benign Acute Childhood Myositis: Presentation

  • Symptoms usually occur during early convalescent period of a viral illness. [Rosenberg, 2016]
  • Symptoms include:
    • Bilateral calf pain
      • Often severe and symmetrical
      • More focal than the diffuse myalgias seen with influenza [Mall, 2011]
      • May have a tip-toe gait
    • Refusal to walk / bear weight
      • Consider this as a cause of Limp or Refusal to Walk along with:
      • Not related to actual weakness
  • Clinical diagnosis can be made in the setting of: [Rosenberg, 2016; Sonmez, 2004]
    • History of recent illness (especially an influenza-like illness)
    • Calf tenderness
    • Normal strength and power
    • Intact tendon reflexes
    • Elevated CPK


Benign Acute Childhood Myositis: Treatment

  • Fluids, Fluids, Fluids (orally or IV)
    • For those with CPK < 3,000 and able to maintain oral hydration, outpatient management may be appropriate with close follow-up.
    • Acute kidney injury is more likely in the setting of dehydration.
  • Pain management
    • With potential concern for kidney injury, NSAIDs may not be the best option.
  • Close Follow-up
    • Repeat CPK levels to ensure improvement is appropriate.
    • Repeat exam to ensure no evolution of actual weakness, decrease reflexes, etc.
    • Those with marked elevated CPK levels, likely benefit from hospitalization to ensure adequate monitoring and hydration.


Moral of the Morsel

  • It’s never “Just a Virus.” Viral illness can lead to significant problems.
  • Check the Urine! Even if it fits this benign condition, think about rhabdomyolysis.
  • Don’t be complacent with Calf Pain. Keep myositis on your Ddx of calf pain, particularly during influenza-season.



Rosenberg T1, Heitner S, Scolnik D, Levin Ben-Adiva E, Rimon A, Glatstein M. Outcome of Benign Acute Childhood Myositis: The Experience of 2 Large Tertiary Care Pediatric Hospitals. Pediatr Emerg Care. 2016 Aug 20. PMID: 27548740. [PubMed] [Read by QxMD]

Hall G1, Schranz CI2. Benign acute childhood myositis–a rare cause of abnormal gait. Am J Emerg Med. 2014 Feb;32(2):193. PMID: 24126025. [PubMed] [Read by QxMD]

Mall S1, Buchholz U, Tibussek D, Jurke A, An der Heiden M, Diedrich S, Schweiger B, Alpers K. A large outbreak of influenza B-associated benign acute childhood myositis in Germany, 2007/2008. Pediatr Infect Dis J. 2011 Aug;30(8):e142-6. PMID: 21753259. [PubMed] [Read by QxMD]

Müjgan Sonmez F1, Cakir M, Yayla S, Boz C. Benign acute childhood myositis. Med Princ Pract. 2004 Jul-Aug;13(4):227-9. PMID: 15181329. [PubMed] [Read by QxMD]

Sean Fox

I enjoy taking care of patients and I finding it endlessly rewarding to help train others to do the same. I trained at the Combined Emergency Medicine and Pediatrics residency program at University of Maryland, where I had the tremendous fortune of learning from world renown educators and clinicians. Now I have the unbelievable honor of working with an unbelievably gifted group of practitioners at Carolinas Medical Center. I strive every day to inspire my residents as much as they inspire me.

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2 Responses

  1. Dr.M.Rajagopalan says:

    Short and crisp. Easy to look through in a busy clinic.

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