Previously, 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, Pericarditis, Mumps, 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:
      • Toxic Synovitis
      • Septic Arthritis
      • Guillain-Barre Syndrome
      • Juvenile Idiopathic arthritis
      • Juvenile Dematomyositis
      • Muscular Dystrophy
      • Fractures
      • Deep Vein Thrombosis
      • Acute Cerebellar Ataxia
      • Malignancy
    • 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.

References