Idiopathic Inflammatory Myositis (IIM)

Idiopathic Inflammatory Myositis (IIM) is a group of autoimmune conditions involving inflammation of muscle fibers used for movement, or the skeletal muscles. IIM is typically reported in adults between the ages of 40 and 60 years, or in children between ages 5 and 15 years. Approximately 2 to 8 cases per million people occur each year for idiopathic inflammatory myopathy.

The specific cause of the disorder is unknown, but genetic and environmental factors may influence the development of IIM. One hypothesis is that specific genetic variations may increase a person’s risk of developing idiopathic inflammatory myopathy, which may be triggered by exposure to specific environmental factors such as medications, or ultraviolet light such as sunlight.

Most cases of IIM are sporadic, but it is noted that some people who suffer from IIM may have close relatives with other autoimmune diseases. Although a small percentage of IIM cases have been reported to be passed on in families, the condition does not have a clear pattern of inheritance.

The most prominent symptom of IIM is muscle weakness that develops gradually over a period of weeks, months, or years. This results in gradual, but progressive loss of strength and muscle tone. Other symptoms may include joint pain and general fatigue. The heart and the lungs can be involved, and an early diagnosis is important to minimize long-term damage.

Other common diseases that are categorized as IIM include polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM). Diagnosis is based on determining muscle weakness upon examination, elevated muscle enzymes, and muscle biopsy. It is important to be properly diagnosed and start therapeutic treatment as soon as possible.

The treatment goals set by a rheumatologist for IIM are to manage symptoms by eliminating inflammation, restore muscle performance, reduce morbidity, and improve the patient’s quality of life. Because this is also categorized as a genetic condition, treatment and management strategies focus on improvement of symptoms associated with IIM.