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Idiopathic inflammatory myopathies (IIM) are a group of diseases that present as muscle weakness and inflamed muscle tissues in muscle biopsy.
This means that there is no external visiible "swelling" of the muscles, and this can only be seen when studying the muscle biopsy under the microscope.
Idiopathic Inflammatory Myopathies explained in first person
Professionals and patients explain how you live with the disease
The most important thing for the patient to know is that these are diseases that we can treat, that we can control, and that the patient can feel well after having treatment.
Sergio PrietoMedical internist
Types of Idiopathic Inflammatory Myopathies
Idiopathic inflammatory myopathies are acquired diseases, in other words, they are not transmitted from parents to children. They can occur at any age and are classified into six major groups:
Dermatomyositis. This is characterised by proximal muscle weakness, in other words, it affects the muscles that are closest to the central part of the body. Patients often have difficulty getting out of a chair, climbing stairs, or raising their arms above their heads. Skin lesions on the face and hands are also typical.
Inclusion body myositis (IBM). It shows in people over 50 and t is characterised by distal muscle weakness, in other words, it affects the muscles furthest from the central part of the body, such as the quadriceps and the flexors of the fingers.
Immune-mediated Necrotising Myopathy (IMNM). This is characterised by rapid onset proximal muscle weakness.
Antisynthetase syndrome (AS). This is characterised by proximal weakness, involvement of the lungs (inflammation or fibrosis), and arthritis (inflammation of the joints), although not all patients have all three symptoms. Patients may also have a fever, Raynaud's phenomenon (colour change in the fingers and toes due to cold or stress), or flaking and cracking of the skin on the hands (known as 'mechanic's hands').
Myositis associated with another autoimmune disease (causing an overlap syndrome). This occurs when a patient has one of the types of myositis mentioned together with another autoimmune disease (including systemic lupus erythematosus, systemic sclerosis, vasculitis, and so on).
Polymyositis. Like IMNM, it presents as proximal muscle weakness, and these are distinguished according to the findings of the muscle biopsy.
How many people does it affect?
Muscle diseases have an annual incidence of 2.1-7.7 cases per million people.
Sergio Prieto GonzálezMedical internistDepartment of Internal Medicine
Published: 25 November 2020
Updated: 25 November 2020
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