Polymyositis & Dermatomyositis

Some muscular diseases like myositis can result in idiopathic lung disease.¹

POLYMYOSITIS/DERMATOMYOSITIS

Polymyositis/dermatomyositis (PM/DM) are idiopathic inflammatory myopathies typically associated with autoantibodies.¹ They commonly overlap with other connective tissue diseases (overlap syndrome), including antisynthetase syndrome.^1,2

Amyopathic dermatomyositis is a rare form of DM that has skin symptoms but no myositis. It is also associated with ILD and can have a poor prognosis.^2,3

This chapter will open with a background on PM/DM, then transition into PM/DM-related ILD.

PM/DM EPIDEMIOLOGY

Prevalence: The current US estimate of people with PM is 31,525, up to 18,850 people have DM.¹

Incidence: 12,350 new cases of PM and 4,500 new cases of DM will be diagnosed this year.¹

Onset of disease typically occurs in individuals between 40 and 55 years of age.^1,4

RISK FACTORS AND MORTALITY

RISK FACTORS

• Women are more likely to develop the disease than men^1,4

MORBIDITY/MORTALITY

• The 5-year survival range is 77%-95%⁵
• ILD is a major cause of morbidity and mortality in PM/DM⁶

PM/DM DIAGNOSTICS

SYMPTOMS

• PM presents with symmetric, proximal skeletal muscle weakness and muscle inflammation. Dermatomyositis includes skin manifestations in addition to these symptoms.^1,2
  • These skin manifestations include Gottron’s sign and heliotrope eruption^1,2
  • Both PM and DM can affect the lungs²

DIAGNOSIS¹⁰

Established diagnosis of PM/DM OR medical history + thorough physical exam + serologies + muscle biopsy.

PM/DM-ILD 

• Between 20% and 66% of patients may get PM/DM-related ILD^2,7
• ILD usually manifests early in myositis, but can appear any time before or after manifestations of skin or muscle⁸
• 3 clinical patterns:
  • Rapidly progressive (associated with high mortality of up to 50%)⁹
  • The more common chronic form that has slowly progressive symptoms⁹
  • Asymptomatic or subclinical form (up to 30% may fall in this category)⁸
• Presence of amyopathic myositis-associated autoantibodies often accompanies rapidly progressive ILD²