Definition   

Disorders caused by an immune response against the body’s own tissues.

Causes and risks   

The immune system protects the body from potentially harmful substances (antigens) such as microorganisms, toxins, cancer cells, and foreign blood or tissues from another person or species. Antigens are destroyed by the immune response, which includes production of antibodies (molecules that attach to the antigen and make it more susceptible to destruction) and sensitized lymphocytes (specialized white blood cells that recognize and destroy particular antigens).

Immune system disorders occur when the immune response is inappropriate, excessive, or lacking. Autoimmune disorders develop when the immune system destroys normal body tissues. This is caused by a hypersensitivity reaction similar to allergies, where the immune system reacts to a substance that it normally would ignore. In allergies, the immune system reacts to an external substance that would normally be harmless. With autoimmune disorders, the immune system reacts to normal "self" body tissues.

Normally, the immune system is capable of differentiating "self" from "non-self" tissue. Some immune system cells (lymphocytes) become sensitized against "self" tissue cells, but these cells are usually controlled (suppressed) by other lymphocytes. Autoimmune disorders occur when the normal control process is disrupted. They may also occur if normal body tissue is altered so that it is no longer recognized as "self." The mechanisms that cause disrupted control or tissue changes are not known. One theory holds that various microorganisms and drugs may trigger some of these changes, particularly in people with a genetic predisposition to an autoimmune disorder.

Autoimmune disorders result in destruction of one or more types of body tissues, abnormal growth of an organ, or changes in organ function. The disorder may affect only one organ or tissue type or may affect multiple organs and tissues. Organs and tissues commonly affected by autoimmune disorders include blood components such as red blood cells, blood vessels, connective tissues, endocrine glands such as the thyroid or pancreas, muscles, joints, and skin.

A person may experience more than one autoimmune disorder at the same time. Examples of autoimmune (or autoimmune-related) disorders include:

• Hashimoto’s thyroiditis
• pernicious anemia
• Addison’s disease
• diabetes
• rheumatoid arthritis
• systemic lupus erythematosus

Symptoms   

Symptoms of autoimmune disease vary widely depending on the type of disease. A group of very non-specific symptoms often accompany autoimmune diseases especially of the collagen vascular type and include:

• Tire easily
• fatigue
• dizziness
• malaise (nonspecific feeling of not being well)
• fever, very low grade temperature elevations

Note: Symptoms vary with the specific disorder and the organ or tissue affected.

Signs and tests   

Signs vary according to the specific disorder. This disease may also alter the results of the following tests:

• platelet aggregation test
• eosinophil count - absolute

Treatment   

The goals of treatment are to reduce symptoms and control the autoimmune process while maintaining the ability to fight disease. The symptoms are treated according to the type and severity.

Hormones or other substances normally produced by the affected organ may need to be supplemented. This may include thyroid supplements, vitamins, insulin injections, or other supplements. Disorders that affect the blood components may require blood transfusions.

Measures to assist mobility or other functions may be needed for disorders that affect the bones, joints, or muscles.

Autoimmunity is controlled through balanced suppression of the immune system. The goal is to reduce the immune response against normal body tissue while leaving intact the immune response against micro-organisms and abnormal tissues. Corticosteroids and immunosuppressant medications (including cyclophosphamide or azathioprine) are used to reduce the immune response.

Prognosis   

The outcome varies with the specific disorder. Most are chronic, but many can be controlled with treatment. Side effects of medications used to suppress the immune system can be severe.

Complications   

• destruction or lack of function of body tissues
• Side effects of medications (See the specific medication.)