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Inflammatory Myopathies (IM)

Overview

Inflammatory myopathies (IM) are a collection of uncommon autoimmune disorders, in which the body’s immune system mistakenly attacks its own skeletal muscles. These conditions may also present with extramuscular symptoms, such as skin rash, joint inflammation, interstitial lung disease (ILD), and heart-related complications. 

There are several forms of inflammatory myopathies, each with distinct features:

  • Dermatomyositis (associated with characteristic skin rash- heliotrope rash, V sign, shawl sign, occasional dysphagia)
  • Overlap myositis (related to connective tissue disorders)
  • Antisynthetase syndrome (ASyS) (presents with multisystem involvement, including arthritis, interstitial lung disease, and myocarditis)
  • Immune-mediated necrotizing myopathy (IMNM) (muscle predominant with severe weakness)
  • Sporadic inclusion body myositis (sIBM) (muscle predominant causing weakness)

People with IM may experience:

  • Muscle pain or cramps
  • Muscle weakness
  • Fatigue
  • Difficulty swallowing/ breathing
  • Skin rash
  • Joint pain and swelling

It is an autoimmune disease with the exact cause yet unknown. Factors that may increase the risk include:

  • Genetic factors: Certain inherited markers, like the HLA 8.1 ancestral haplotype is an important risk factor in some populations.
  • Environmental factors: These include:
    • Exposure to ultraviolet (UV) light
    • Smoking
    • Infections
    • Vitamin D deficiency
    • Exposure to certain pollutants
    • Exposure to medications
    • Exposure to inhaled particles
    • Exposure to chemical agents
    • Exposure during pregnancy and infancy
  • Other factors: Certain medications, such as statins, can increase HMGCR expression in muscles, which may worsen autoimmunity against muscle tissue

Doctors use a combination of tests to diagnose IM:

  • Clinical examination: to check muscle strength and function
  • Blood tests: to determine serum enzyme levels using the Myositis panel which includes the auto-antibodies responsible for muscle inflammation and weakness.
  • Electromyography (EMG): Tests electrical activity of muscles
  • Muscle biopsy
  • Muscle MRI: Identifies inflammation patterns and helps target biopsy site

Treatment focuses on reducing inflammation, controlling the immune attack, and improving daily function:

  • Corticosteroids: first-line treatment to reduce inflammation
  • Immunosuppressive medications: to reduce immune activity (e.g., methotrexate, azathioprine)
  • Physiotherapy/speech therapy: to improve mobility and swallowing function
  • Management of associated systemic features: treating associated conditions like lung or heart involvement

Seek medical attention if you experience:

  • Persistent muscle weakness or cramps that worsen over weeks
  • Difficulty climbing stairs, lifting objects, or raising arms
  • Unexplained skin rash with weakness

Since IM is autoimmune and often unpredictable, it cannot always be prevented. However, you can:

  • Avoid smoking and minimise exposure to pollutants/chemicals
  • Limit unnecessary medications known to trigger symptoms (e.g., statins if advised by your doctor)
  • Protect skin from excessive UV exposure

For diagnosis and management of IM, consult a Neurologist (specialist in brain and nerve disorders).

Disclaimer:

The information in this Health Library is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional with any questions about a medical condition or before starting any treatment. Use of this site and its content does not establish a doctor–patient relationship. In case of a medical emergency, call your local emergency number or visit the nearest emergency facility immediately.