Autoimmune Diseases

AUTOIMMUNE DISEASES

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune diseasecharacterized by loss of self-tolerance and production of autoantibodies. Females are affected much more often than males (M:F = 1:9); peak incidence is age 20–45; and African Americans are affected more often than Caucasians. The mechanism of injury in lupus is a mix of type II and III hypersensitivity reactions.

·              Important autoantibodies that may be detected in the sera from lupus patients include antinuclear antibody (ANA) (>95%); anti-dsDNA (40–60%); anti-Sm (20–30%); antihistone antibodies; nonhistone nuclear RNA  proteins; and blood cells.

·              SLE affects many organ systems

o     Hematologic (type II hypersensitivity reaction) manifestations can include hemolytic anemia, thrombocytopenia, neutropenia, and lymphopenia.

o     Skeletal manifestations include an arthritis characterized by polyarthralgia and synovitis without joint deformity (type III hypersensitivity reaction).

o     Skin (type III hypersensitivity reaction) manifestations can include a malar “butterfly” rash; maculopapular rash; and ulcerations and bullae formation.

o     Serosal surfaces may also be affected, with resulting pericarditis, pleuri-tis, or pleural effusions (type III hypersensitivity reaction).

o     Central nervous system manifestations include focal neurologic symp-toms, seizures, and psychosis (type III hypersensitivity reaction).

o     Cardiac manifestations include Libman-Sacks endocarditis (nonbacte-rial verrucous endocarditis) (type III hypersensitivity reaction).

·            Of particular importance are the renal manifestations (type III hypersensitiv-ity) classified by the Society of Nephrology/Renal Pathology Society as follows.

Class I: minimal mesangial lupus nephritis

Class II: mesangial proliferative lupus nephritis

Class III: focal (< 50%) lupus nephritis

Class IV: diffuse (> 50%) lupus nephritis

Class V: membranous lupus nephritis

Class VI: advanced sclerosing lupus nephritis

·              Lupus is treated with steroids and immunosuppressive agents. It tends to have a chronic, unpredictable course with remissions and relapses. The 10-year survival is 85%, with death frequently being due to renal failure or infections.

Sjögren syndrome (sicca syndrome) is an autoimmune disease characterized bydestruction of the lacrimal and salivary glands, resulting in the inability to produce saliva and tears. Females are affected more often than males, with typical age 30–50.

Clinical manifestations include keratoconjunctivitis sicca (dry eyes) and corneal ulcers; xerostomia (dry mouth); and Mikulicz syndrome (enlargement of the sali-vary and lacrimal glands). Sjögren syndrome is often associated with rheumatoid arthritis and other autoimmune diseases. The characteristic autoantibodies are the anti-ribonucleoprotein antibodies SS-A (Ro) and SS-B (La). There is an increased risk of developing non-Hodgkin lymphoma.

Scleroderma (progressive systemic sclerosis) is an autoimmune disease character-ized by fibroblast stimulation and deposition of collagen in the skin and internal organs. It affects females more than males, with typical age range of 20 to 55 years. The pathogenesis involves activation of fibroblasts by cytokines interleukin 1 (IL-1), platelet-derived growth factor (PDGF), and/or fibroblast growth factor (FGF) with the resulting activated fibroblasts causing fibrosis.

·              Diffuse scleroderma has anti-DNA topoisomerase I antibodies (Scl-70) (70%),widespread skin involvement, and early involvement of the visceral organs. Organs that can be affected include the esophagus (dysphagia), GI tract (mal-absorption), lungs (pulmonary fibrosis which causes dyspnea on exertion), heart (cardiac fibrosis which may manifest as arrhythmias), and kidney (fibrosis that may manifest as renal insufficiency).

·              Localized scleroderma (CREST syndrome) has anti-centromere antibodies,skin involvement of the face and hands, late involvement of visceral organs, and a relatively benign clinical course.

Mixed connective tissue disease is an overlap condition with features of systemiclupus erythematosus, systemic sclerosis, and polymyositis. Antiribonucleoprotein antibodies are nearly always positive.