Myositis

What is Myositis?
  • Myositis is a term referring to a group of disorders characterized by skeletal muscle inflammation. Presentation typically presents as progressive, symmetric muscle weakness. May involve other organs including the lungs, joints, hear, and skin.
What are the types of Myositis?
  • Dermatomyositis
  • Immune-mediated necrotizing myopathy
  • Antisynthetase syndrome
  • Inclusion body myositis
  • Overlap myositis
What are common symptoms and characteristics of myositis?
  • Dermatomyositis
    • Proximal, symmetric muscle weakness
    • Skin rashes (Gotton’s papule, “shawl sign”, “V-sign”, “mechanic’s hands”
    • Elevated muscle enzymes (CK, aldolase)
    • Presents as classic (skin and muscle), myopathic (skin without muscle), or hypomyopathic (skin with subclinical muscle)
    • Increased malignancy risk
    • Can involve other organs
  • Immune-mediated necrotizing myopathy
    • Severe proximal muscle weakness
    • Elevated CK (muscle enzyme)
  • Antisynthetase syndrome
    • Proximal muscle weakness
    • Interstitial lung disease
    • Raynaud’s phenomenon
  • Inclusion Body Myositis
    • Older adults
    • Proximal and distal muscle weakness
  • Overlap Myositis
    • Associated with other connective tissue diseases
What other parts of the body are affected?
  • Dermatomyositis
    • Lungs (i.e. interstitial lung disease)
    • Joints (i.e. pain, no erosions)
    • Gastrointestinal tract (i.e. trouble swallowing)
    • Heart (i.e. arrhythmia, myocarditis, heart failure)
    • Calcinosis (calcium deposits under the skin)
    • Raynaud’s phenomenon
  • Immune-mediated necrotizing myopathy
    • Lungs (i.e. interstitial lung disease)
  • Antisynthetase syndrome
    • Lung (i.e. interstitial lung disease)
    • Joints (i.e. symmetric joint pain, no erosions)
    • Skin (i.e. mechanic’s hands, rashes)
    • Raynaud’s phenomenon
    • Heart (i.e. pericardial effusion, pulmonary hypertension)
  • Inclusion body myositis
    • Gastrointestinal tract (i.e. trouble swallowing)
    • Lungs (i.e. respiratory failure, sleep-disordered breathing)
    • Nervous system (i.e. peripheral neuropathy)
    • Sjogren’s syndrome
    • Blood cancers
  • Overlap myositis
    • Features of associated connective tissue disease
    • Lungs (i.e. interstitial lung disease)
    • Joints (i.e. pain without erosions)
    • Skin (i.e. sclerodactyly)
    • Raynaud’s phenomenon
    • Gastrointestinal tract (i.e. trouble swallowing)
    • Heart
How is Myositis diagnosed?
  • Physical exam
  • Elevated muscle enzymes (CK, aldolase)
  • EMG nerve conduction study
  • Muscle biopsy
  • Specific autoantibodies
    • Dermatomyositis
      • MI-2: weakness, high CK, inflammation on muscle biopsy
      • TIF1γ: classic skin rash, increased cancer risk, trouble swallowing, red patch on the soft palate
      • NXP2: subcutaneous swelling, calcinosis, trouble swallowing, distal arm and leg weakness, finger extensor weakness, increased cancer risk, intestinal vasculopathy
      • MDA5: myopathic, rapidly progressive interstitial lung disease
      • SAE: severe skin disease, angel wing rash, mild muscle weakness, mild interstitial lung disease, possible pulmonary nodules
    • Anti-Synthetase Syndrome
      • Jo-1: myositis, arthritis, mechanic’s hands, Raynaud’s, interstitial lung disease
      • PL7: myositis, arthritis, mechanic’s hands, Raynaud’s, interstitial lung disease
      • PL12: myositis, arthritis, mechanic’s hands, Raynaud’s, interstitial lung disease
      • EJ: myositis, arthritis, mechanic’s hands, Raynaud’s, interstitial lung disease
      • OJ: myositis, arthritis, mechanic’s hands, Raynaud’s, interstitial lung disease
    • Necrotizing Myopathy
      • HMGCR: associated with statin exposure, severe weakness, very high CK, necrosis on muscle biopsy
      • SRP: rapidly progressive weakness, very high CK, necrosis on muscle biopsy, cardiac involvement (myocarditis), trouble swallowing
    • Inclusion Body Myositis
      • NT5c1A/cN1A: typically male patients over the age of 50, asymmetric muscle weakness, rimmed vacuoles on muscle biopsy
How is Myositis treated?
  • Glucocorticoids
  • 1st line
    • methotrexate
    • azathioprine (Imuran)
  • 2nd line
    • mycophenolate (CellCept)
    • IVIG
    • Rituxan (rituximab)
    • cyclosporine/tacrolimus
    • w/ severe interstitial lung disease
      • mycophenolate (CellCept)
    • w/ HMGCR and severe trouble swallowing
      • IVIG
    • w/ ILD and anti-SRP
      • Rituxan (rituximab)
  • Refractory disease
    • cyclophosphamide
    • tofacitinib