Reaching an accurate diagnosis is often a long and frustrating process for myositis patients and their doctors. Myositis diseases are rare and complex, with poorly understood origins and features that may be similar to other disorders. As such, there is not a single lab test that can easily diagnose any of the forms of myositis. Is such a situation, physicians often rely on diagnostic criteria to determine a diagnosis.

Diagnostic criteria are a set of signs, symptoms, and tests used to guide the care of individual patients. They are usually broad and must reflect different features of a disease in order to accurately identify as many people with the condition as possible.

While it is ideal to have criteria that are validated by research evidence, at this point in time, researchers are still working to develop and validate diagnostic criteria for myositis diseases. Until this process is completed, physician usually establish a diagnosis based on their own experience of clinical signs and symptoms, available clinical tests, and knowledge about the epidemiology of their geographical area.

The following diagnostic criteria have been developed based on research data in combination with expert clinical experience. These are criteria most often used as a guide to establish a specific diagnosis. Before diagnosing any form of myositis, all other myopathies must be ruled out.

Inclusion body myositis


Amyopathic dermatomyositis


Necrotizing myopathy
(also known as immune-mediated necrotizing myopathy or necrotizing autoimmune myopathy)

Juvenile dermatomyositis