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Normally the immune system controls the body's defenses against infection. In systemic lupus erythematosus (SLE) and other autoimmune diseases, these defenses are turned against the body and rogue immune cells attack tissues. Antibodies may be produced that can react against the body's blood cells, organs, and tissues. These lead immune cells to attack the affected systems, producing chronic disease.
The mechanism or cause of autoimmune diseases is not fully known, but many researchers suspect it occurs following infection with an organism that looks similar to particular proteins in the body, which are later mistaken for the organism and wrongly targeted for attack.
The disease affects 9 times as many women as men. It may occur at any age, but appears most often in people between the ages of 10 and 50 years. SLE may also be caused by certain drugs. When this occurs, it is known as drug-induced lupus erythematosus and it is usually reversible when the medication is stopped.
The course of the disease may vary from a mild episodic illness to a severe fatal disease. Symptoms also vary widely in a particular individual over time and are characterized by periods of remission and exacerbation. At its onset, only one organ system may be involved. Additional organs may become involved later. The following organ system manifestations may be seen, but other manifestations are possible.
Musculoskeletal
Almost all people with SLE have joint pain and most develop arthritis. Frequently affected joints are the fingers, hands, wrists, and knees. Death of bone tissue can occur in the hips and shoulders and is frequently a cause of pain in those areas.
Skin
A "butterfly" rash over the cheeks and bridge of the nose affects about half of those with SLE. The rash is usually worsened by sunlight. A more diffuse rash may appear on other body parts that are exposed to the sun. Other skin lesions or nodules can also occur.
Kidney
Some people with SLE have deposits of protein within the cells (glomeruli) of the kidney. However, less than 50% have lupus nephritis as defined by persistent inflammation (irritation and swelling) in the kidney. These patients may eventually develop renal failure and require dialysis or kidney transplantation.
Nervous system
Neurologic disorders can affect up to 25% of those with SLE. Mild mental dysfunction is the most common symptom, but any area of the brain, spinal cord, or nervous system can be affected. Seizures, psychosis, organic brain syndrome, and headaches are some of the varied nervous system disorders that can occur.
Blood
Blood disorders can affect up to 85% of those with SLE. Venous or arterial blood clots can form and are associated with strokes and pulmonary embolism, or pregnancy loss. Predisposition to blood clots, or less commonly bleeding, occurs due to antibodies against lipids involved in blood clotting and is referred to as anti-phospholipid antibody syndrome (APS). (See Lupus anticoagulant.) Often platelets are decreased which may cause bleeding or clotting problems. Anemia of chronic disease often develops at some point in the course SLE.
Heart
Inflammation of various parts of the heart may occur as pericarditis, endocarditis, or myocarditis. Chest pain and arrhythmias may result from these conditions.
Lungs
Pleurisy, an inflammation of the lining of the lung, and pleural effusions, a fluid collection between the lung and its lining, can occur as a result of SLE. Chest pain and shortness of breath are frequently results of these disorders.
African Americans and Asians are affected more often than people from other races.
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