Benign acute childhood myositis
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Benign acute childhood myositis (BACM), sometimes referred to as viral myositis or influenza-associated myositis is a striking cause of childhood immobility, which is typically self-limiting and benign.

It often presents in school-age children, a few days after a viral infection (typically an URTI).

It is more common in boys.

Treatment is supportive and it generally resolved within a few days.

Epidemiology and Aetiology

  • Epidemiology is unknown
  • It is thought to be under-diagnosed
  • Typically occurs several days after a viral infection
    • Influenza is the most common causatory organism, particularly influenza B


  • Calf pain
    • Pain usually almost always confined solely to the calves
  • Bilateral
  • Way result in a characteristic tip-toe walk, or refusal to walk
    • Children often crawl to get around
  • Extending the knees causes calf pain
  • Acute onset
    • E.g. patient awakes with symptoms, or onset over the course of an hour or two
  • Children otherwise systemically well
  • Symptoms often progressive, e.g.
    • Day one – complaining of calf pain
    • Day two and three – refusing to walk – crawling on all 4s
    • Day three – tip-toe walking
    • Day 4 – return to normal gait and mobility
  • Tender calves on examination
  • Rarely rhabdomyolysis can occur


  • Diagnosis usually clinical
  • Often quite distressing for parents
  • Due to under-recognition of the condition, there may be over-investigation for serious causes
  • Bloods
    • May show raised creatine kinase (CK)
    • Not usually indicated
  • Nasopharyngeal swab for influenza PCR
    • May confirm the diagnosis of influenza
    • Again, not usually needed



  • Reassure parents
  • Typically time for resolution of symptoms is 3 days
  • Simple analgesia
    • e.g. paracetamol 15mg/Kg QID
    • +/- ibuprofen 10mg/Kg TDS
  • Safetynetting for worsening symptoms, fevers, systemically unwell, or dark urine (rhabdomyolysis)

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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