Myositis (peds)

Background

• Influenza is one of the most common causes of viral myositis
• Rhabdo is unusual but has been reported.

Clinical Features

• Patients usually have a history of recent illness (fever, URI symptoms, fever, etc)
• Significant myalgias as starting to improve from constitutional symptoms
  • Most commonly lower legs
  • Can have pain and tenderness in other muscle groups (thighs, arms)
• Usually look well, but will sometimes walk with wide gait and on their toes
  • When lying in bed, will often keep toes pointed with pain in calves upon dorsiflexion

Differential Diagnosis

Myalgia

• Infection:
  • Viral infection (e.g. Influenza)
  • Bacterial infection
  • Spirochete infection (E.g. Dengue fever; Trichinella)
• Drugs:
  • Statins
  • Bisphosphonates
  • Corticosteroids
  • Ciprofloxacin
  • Clofibrate
  • Colchicine
  • Chloroquine
  • Emetine
  • Aminocaproic acid
  • Zidovudine
  • Bretylium
  • Penicillamine
  • Drugs causing hypokalemia
• Metabolic disorders:
  • Vitamin D deficiency
  • Mitochondrial myopathy
  • Scurvy
  • Osteomalacia
• Fibromyalgia
• Endocrine:
  • Hypothyroidism
  • Hyperthyroidism
  • Cushing’s syndrome
  • Adrenal insufficiency
  • Hyperparathyroidism
• Polymyalgia rheumatica
• Rhabdomyolysis
• Myositis
  • Polymyositis
  • Dermatomyositis
  • Myositis (peds)
• Systemic lupus erythematosus
• Rheumatoid arthritis
• Inclusion body myositis
• Sarcoidosis
• Scleroderma
• Sjögren’s syndrome
• Psychiatric (e.g. somatic manifestations of depression)
• Domestic abuse
• Crush injury
• Lyme disease
• Ehlers-Danlos syndrome(hypermobility syndrome)
• HIV myopathy
• Hypophosphatemia
• Hypokalemia
• Hypothermia
• Prolonged immobility
• Strenuous exercise (overuse) or heat stroke
• Seizure
• Severe volume contraction
• Alcoholism
• Muscular dystrophy
  • Duchenne
  • Becker
  • Limb-girdle
  • Facioscapulohumeral
  • Myotonic dystrophy
  • Myotonia congenita
• Compartment syndrome; Muscle infarction
• Neuropathic
• Chronic fatigue syndrome
• Vasculitis
• Sarcocystosis
• Spinal stenosis
• Diabetic lumbosacral plexopathy

Evaluation

Workup

• Total ck
• UA (for myoglobin)