Idiopathic Inflammatory Myopathy

What is Idiopathic Inflammatory Myopathy?
Idiopathic Inflammatory Myopathy (IIM) is a group of muscle disorders with symmetrical proximal muscle weakness of the limbs. Amongst these rare types of myopathies, the 2 most common types are Polymyositis and Dermatomyositis. Other types are Overlap Myositis, Inclusion Body Myositis and Necrotising Myopathy. There are various etiologies including autoimmune, paraneoplastic, infective, and drug-induced.
What are the Symptoms of Inflammatory Myositis?
The most common symptom is proximal muscle weakness of the shoulders, thighs and neck, or difficulty in swallowing. But there may be other non-muscular symptoms such as fatigue, loss of appetite, loss of weight, fever, rashes, joint pain and stiffness, reduced effort tolerance, and cough. Due to the diverse symptoms including the non-muscular ones, diagnosis may be delayed initially.
There is a subtype of Dermatomyositis with positive Anti-MDA5 Antibody, usually presenting with rashes but minimal weakness. This subtype is associated with rapidly progressive interstitial lung disease, with high mortality rate if not recognised and treated early.
What are the treatments available for Inflammatory Myositis?
At diagnosis, various blood and imaging tests are carried out to screen for malignancy, as dermatomyositis is highly associated with cancer.
The mainstay of treatment is corticosteroids and other immunosuppressants. Patients with more aggressive disease may be treated with newer therapies such as anti-CD20 and Janus Kinase (JAK)-inhibitors.