## INTRODUCTION AND EPIDEMIOLOGY

Key Clinical Questions

• Does this patient have systemic lupus erythematosus (SLE)?

• Has SLE disease activity led to this patient’s hospitalization?

• How should flares of SLE be managed?

• How does treatment of other diseases affect the status of SLE?

• What are possible adverse consequences of the treatment of SLE?

• How should medications for SLE be managed upon hospital discharge?

Systemic lupus erythematosus (SLE) is an autoimmune disease that affects about 1 in 2000 individuals, most commonly women of childbearing age. SLE can manifest itself in any organ system, and disease activity varies over time. Both the incidence and severity of SLE are increased in individuals of African or Caribbean descent, as well as in Hispanic populations within the United States.

While modern 5-year survival rates for SLE are around 95%, and 20-year survival rates are around 80%, these higher survival rates have come with increased hospitalization rates. In one retrospective analysis, more than half the patients in a lupus cohort were hospitalized over the previous 2 years. Lupus is associated with increased health care expenditure, and the in-hospital mortality rate ranges from 3% to 8%. In one study, the average length of stay for inpatients with lupus was 6 days (median cost $10,000). Among those who died in the hospital, the average length of hospitalization was 12 days (average cost around$25,000). The most common causes of inpatient mortality are infection, organ failure secondary to active SLE (ie, renal failure, CNS involvement, pulmonary hemorrhage), and cardiovascular disease.

The most common reason for hospitalization in patients with SLE is disease flare. Other common reasons for admission include complications of SLE or its treatment, such as infections, cardiovascular events and thromboembolic disease. Individuals with SLE are at high risk for premature atherosclerosis and may be admitted with chest pain, acute coronary syndromes, or cerebrovascular accidents. Lupus may also present as a new diagnosis in patients with pericarditis, glomerulonephritis, or neurologic disease.

## PATHOPHYSIOLOGY

Autoimmune diseases are thought to result from an environmental trigger, such as infection, sunlight, or smoking, activating an abnormal immune response in a genetically susceptible individual.

The hallmark of SLE is serum autoantibodies against nuclear proteins. Autoantibodies may arise from defective clearance of apoptotic cells. When cells undergo apoptosis, internal proteins are displayed on surface blebs. If apoptotic cells are not cleared, nuclear material is exposed to the immune system, which may become sensitized. Certain complement component deficiencies, namely of C4 and C1q, are associated with an increased incidence of SLE; this may relate to the role of complement activation in clearing apoptotic cells and foreign antigens.

Autoantibodies can damage tissues through direct binding to cell surfaces with subsequent immune system activation, or by deposition of immune complexes in tissues. Immune complexes are not effectively cleared in patients with SLE, due to quantitative and qualitative deficiencies in Fc ...

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