Myositis usually begins gradually, but can take a variety of forms. Sometimes the first sign is an unusual rash. Sometimes patients may start to trip or fall more frequently. Other signs include muscle weakness and pain, intense fatigue, and trouble climbing stairs or reaching over the head. Frequently, patients explain these symptoms away as signs of “getting old.” But myositis is a very real and often serious condition that needs to be taken seriously.

Types of myositis

There are several different forms of myositis. Review each of the myositis conditions below to learn the differences and similarities among the different types.

Inclusion body myositis

Inclusion body myositis (IBM) is the most common form of myositis in people over 50. Symptoms are slow to progress and include difficulty walking or climbing stairs.

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Dermatomyositis (DM) affects people of all ages and sexes, but is more common among women. It shows up as muscle weakness along with a rash on the eyelids, cheeks, nose, back, upper chest, elbows, knees, and/or knuckles.

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Polymyositis usually occurs in people over the age of 20, affecting more women than men. The biggest symptom is muscle weakness that begins in the trunk (neck, hips, back and shoulders) and worsens over time.

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Necrotizing myopathy (NM)

Also called necrotizing autoimmune myopathy (NAM) or immune-mediated necrotizing myopathy (IMNM), necrotizing myopathy involves muscle weakness with evidence of muscle cell death (necrosis). It was once grouped under the polymyositis diagnosis, but is now considered a separate form of myositis.

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Juvenile myositis

Found in children under the age of 18, juvenile myositis (JM) is characterized by muscle weakness in the neck, shoulders, back, and torso. Juvenile dermatomyositis also has a red, patchy skin rash.

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As is the case for many rare diseases, these types of myositis can be difficult to diagnose, often requiring extensive testing and a muscle and/or skin biopsy. Learn more about the diagnosis process and work with your doctor to determine the cause of your symptoms.