Inflammatory myositis is a systemic autoimmune disease that has four forms:
- Necrotizing Autoimmune Myositis
- Inclusion Body Myositis
Inflammatory myositis is more common in African-Americans compared to caucasians and in woman compared to men. Polymyositis primarily affects adults in their 30’s to 50’s. Dermatomyositis commonly affects children ages 5-15 and adults ages 45-65. Myositis can occur in combination with other autoimmune diseases. The exact cause is unknown, but we do know that it is an autoimmune disease (the body’s own immune system attacks the muscles) and in some cases the skin.
Myositis is characterized by the onset of chronic, severe weakness in muscles close to the trunk – the upper arms/shoulders, thighs and sometimes the neck. Weakness is due to muscle inflammation and subsequent muscle damage. While weakness is the most prominent symptom, muscle soreness can also occur. Patients may notice difficulty getting out of a chair, putting things away in overhead cabinets, or trouble climbing stairs due to weakness rather than pain. Other symptoms can include shortness of breath from lung inflammation, joint pain, Raynaud’s syndrome (finger color changes and numbness in cold weather), and trouble swallowing. Patients with dermatomyositis often develop several different kinds of rashes including one on the hands (Gottron’s papules), a violet discoloration or swelling around the eyes (heliotrope), and/or across the back and chest (shawl rash). This rash is worsened by sun exposure.
The diagnosis of inflammatory myositis relies on the history (e.g. how fast are the symptoms progressing?), physical exam, lab tests (e.g. how high are the muscle enzymes or tests that measure levels of muscle inflammation in the blood?), imaging such as MRI of the thigh muscles that can reveal muscle inflammation, nerve conduction studies and a muscle biopsy. The above results will help your rheumatologist (sometimes working with a neurologist) to exclude other diseases that can cause muscle weakness and thereby mimic inflammatory myopathies. Such mimickers include thyroid disease, toxin-induced myopathies (e.g. associated with the use of cholesterol lowering medications called statins), neuromuscular disorders (e.g. muscular dystrophy), infections, and genetic conditions such as metabolic myopathies (e.g. McArdle’s, mitochondrial myopathies).
It is important to establish the correct cause of the muscle weakness because each type of myositis is treated differently, and each has a different prognosis. Importantly, polymyositis and dermatomyositis can be associated with cancer. Your doctor will take a thorough history to make sure you are up-to-date with age-appropriate cancer screening (e.g. colonoscopy if you are over age 50).
Additional information on inflammatory myositis can be found Here.
Infusion treatment medications include: