What are the types of myositis?

There are five forms of myositis. They are:

• Sporadic inclusion body myositis (sIBM): The most common form, it tends to impact those older than 50 and more often in men than women. It progresses more slowly than other forms and manifests in the smaller muscles of the hands and forearms, impacting a person’s grip and fine motor skills. Larger muscles decline as well.
• Dermatomyositis (DM): It is more common among women. It is easiest to diagnose because it emerges on the skin before muscle weakness begins, whether through scaly, swollen patches or a rash that appears on the eyelids, cheeks, nose, back, upper chest, elbows, knees and knuckles.
• Polymyositis (PM):  Striking after age 20, this affects more women than men. Not only does it hamper a patient’s ability to walk, run, or get up after a fall, but it often causes a chronic dry cough or difficulty swallowing (dysaphgia).
• Necrotizing myopathy: This recently defined form is also called necrotizing autoimmune myopathy or immune-mediated necrotizing myopathy. (It was grouped under polymyositis but is now considered separate.)  It is marked by muscle cell death (necrosis). This manifests in muscle weakness but patients also complain of fatigue and overall general tiredness.
• Juvenile Myositis (JM): The term for any version of myositis found in children under the age of 18. Typically pediatric patients have dermatomyositis or polymyositis forms. Some additional symptoms include trouble lifting the head, a hoarse voice, stomach aches, hardened lumps under the skin and irritability. See our Juvenile Myositis Clinic page for more information about juvenile myositis and how to make an appointment.