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 M. Fox
Sean M. 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 renowned 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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  1. Hello, My son had this when he was in kindergarten. We were so scared. Took him to Montefiore Hospital in the Bronx. He was admitted and they checked his blood and urine. The ck levels were high, and he couldn’t walk because of his calf pain. He was hooked to an IV and was there for 3 days or so. Now, in 3rd grade he has it again!!! He has strep and tested positive for FLU. We called Pediatrician and he recommended drinking lots of fluids like gatorade and hydrate. And rest. But as a parent, at what point should I take him to the hospital. How long can he drink before he’s back to normal(walking) I can’t check the cpk whatever levels at home. Also, is it normal for this to reoccur?? it has been 3 times already. I appreciate your response, for I find this to be a very strange illness. I never saw this growing up and don’t understand it.

    Thank you

  2. I’ve been a nurse for 24 yrs and never seen this until today with my 5 yr old grandson who presented with inability to stand and crying in pain and only able to tiptoe.. because of pain. 2 wks ago he had traumatic amputation of finger, so my first thought was something related to this…but finger looks good. But 4 days ago he started treatment for flu….all exams while he was sitting or lying down were negative.. thank God for a wonderful Doctor that realised what was going on!! Just today…. so hopefully this is what it is and nothing more serious!!!

  3. One of the little girls that I watch just got a diagnosis of this illness. She’s had her first ear infection and a cold and the got another cold 2 weeks later & woke up from a nap barely walking. Her parents took her in to the Dr right away after seeing a newcast about afm and the Dr was concerned enough about that to do lab tests. Thanks for such a clear cut explanation so I could learn what she has. I’ve never heard of this.

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