Acquired diseases of connective tissue
The acquired connective tissue diseases, which are described in detail in this section, display certain common clinical features, including inflammation of the joints (polyarthralgia and arthritis), serous (fluid-exuding) membranes (pleurisy and pericarditis), and small blood vessels (vasculitis) and a high frequency of involvement of various internal organs that are particularly rich in connective tissue (e.g., the lungs). The walls of inflamed blood vessels, portions of which may become necrotic (i.e., may die), are often found to contain characteristic deposits of hyaline (translucent) material called fibrinoid because staining with dyes (e.g., eosin) reveals tinctorial properties similar to fibrin (a fibrous protein that forms the lattice of blood clots).
A number of observations suggest that acquired connective tissue diseases are autoimmune diseases—i.e., diseases that result from reactions against components of the body as if they were foreign substances. In general terms these observations are that: (1) there are abnormally high levels of immunoglobulins in the blood; the immunoglobulins, also called gamma globulins, consist wholly or chiefly of antibodies; (2) these antibodies include several directed against particular serum proteins and other components of the affected person’s own tissues; (3) there are complexes (combinations) of these antibodies and their antigens at the sites of tissue damage; (4) at the sites of tissue damage there are also aggregations of the cells (plasma cells and lymphocytes) that are responsible for the production of antibodies; (5) there is a favourable response to treatment with medications, such as corticosteroid hormones, known or believed to inhibit the production of antibodies; (6) connective tissue diseases are associated with other disorders known or suspected to be the result of an aberrant immune system.
Antibody-antigen interactions may result in the destruction of red or white blood cells or platelets or may inactivate circulating hormones or enzymes. The antibody-antigen complexes may be deposited in the walls of blood vessels and there combine with a substance in the blood called complement, with a variety of injurious effects, including those seen in serum sickness and in rheumatoid arthritis and the kidney damage seen in systemic lupus erythematosus (see below Systemic lupus erythematosus). Last, the interaction may result in cellular immunity, which plays an important role in certain autoimmune disorders that involve solid organs, as well as in transplant rejection and cancer immunity.
Rheumatoid arthritis
Rheumatoid arthritis is a chronic disease in which inflammation of the peripheral joints occurs. The disease process within the joints begins as an inflammation of the synovium (joint-lining tissue). In most cases there is an increase, often considerable, in the amount of synovial (joint) fluid. Other manifestations of the disorder include blood-vessel inflammation in the form of tiny areas of necrosis in the fingertips, chronic leg ulcers and lesions in the peripheral nerves, inflammation of the pericardium and of the sclerae, inflammation and nodule formation in the lungs and pleura (tissue covering the lungs), anemia, enlargement of the lymph nodes, and Sjögren, or sicca, syndrome (see below).
Systemic lupus erythematosus
Systemic lupus erythematosus (SLE) is a chronic inflammatory disease of unknown cause that affects, either singularly or in combination, the skin, joints, kidneys, nervous system, and membranes lining body cavities and often other organs as well. The disease has a tendency toward remissions and exacerbations and a multitude of immunologic abnormalities, including antibodies that react with components of cell nuclei, as well as antibodies directed against circulating proteins, blood cells, and solid organs. The disease may develop at any period of life but appears with highest frequency during the second to fourth decades. Most affected persons are women; the disorder is three times more common in black women than in white women. Systemic lupus erythematosus exists in many forms, from the very mild to severe and rapidly fatal. The annual incidence of the disease has been estimated to be at least three to six cases per 100,000 population.
The identification of systemic lupus erythematosus is based primarily on certain clinical findings, the most specific and frequent of which include: (1) facial erythema (reddening), which often takes the form of a butterfly-shaped rash over the bridge of the nose and the cheeks and which occurs in only a minority of adults with the disease, (2) discoid lupus, an erythematous raised patchy eruption that heals with scarring and atrophy of the skin and may be found anywhere on the body, (3) Raynaud syndrome (see below), (4) photosensitivity, manifested by unusual skin reaction after exposure to sunlight, (5) nondeforming arthritis, (6) inflammation of the kidneys (glomerulonephritis), (7) inflammation of the chest lining (pleurisy) or of the membranous sac enclosing the heart (pericarditis), or both, and (8) central nervous system involvement, in the form of psychosis or convulsions. In addition to specific organ involvement, affected persons also have constitutional symptoms—including fever, weakness, fatigability, and weight loss—that are often the first manifestation of illness.
Some degree of anemia is found in most persons with the disease, often the result of an increased rate of red cell destruction attributable to antibodies that coat the cell and damage its membrane. Low white blood cell counts (leukopenia) and platelet counts (thrombocytopenia) are also characteristic; these too can often be traced to the presence of specific autoantibodies. Abnormal bleeding may result from thrombocytopenia or from an antibody that combines with and inactivates certain plasma proteins (clotting factors) involved in blood coagulation. Rheumatoid factor (see above Rheumatoid arthritis) occurs in about 25 percent of cases. Most important from the standpoint of diagnosis are the antibodies that combine with various components of cell nuclei. One or more of these antinuclear antibodies are present in virtually all persons with active disease. The first of these antibodies to be recognized was the lupus erythematosus cell factor, discovery of which permitted detection of previously obscure and unrecognized forms of systemic lupus erythematosus.
The compound thus formed is avidly ingested by certain phagocytic (particle-engulfing) white blood cells called neutrophilic leukocytes, which, distended by the compound of antibody and of lymphocyte-nucleus component, are the characteristic lupus erythematosus cells. Two antibodies fairly characteristic of lupus erythematosus react specifically with deoxyribonucleic acid (DNA) and double-stranded ribonucleic acid (RNA) of cell nuclei. The presence of these two antibodies is associated with an active disease, in particular with inflammation of the kidney and with skin and brain lesions.
Evidence strongly suggests the possibility that one or more viruses may be the ultimate source of the antigenic stimulation responsible for the development of these autoantibodies.
The treatment of systemic lupus erythematosus aims to reduce or control inflammation and to limit damage to vital organs. Salicylates (aspirin) are used to relieve pain, particularly when joints are involved, and to reduce fever. In most cases, it is necessary to employ corticosteroid hormones or NSAIDs (nonsteroidal anti-inflammatory drugs) to reduce inflammation in acute crises of the disease. Certain antimalarial medications, such as chloroquine and hydroxychloroquine, have been found to exert an anti-inflammatory effect on skin and joint lesions and are widely used for the treatment of milder forms of the disease. Immunosuppressive medications are prescribed for patients whose kidneys or central nervous systems are affected by the disease.
The course of systemic lupus erythematosus is highly variable. Acute episodes occur, but more commonly the disease gives rise to a subacute or chronic illness that smolders for many months or years, subject to spontaneous remissions and exacerbations. There may be long intervals (up to 20 years or more) in which the affected person is entirely free of symptoms, with little or no evidence of the disease aside from serologic abnormalities, which tend to persist indefinitely. In most cases the prospects of survival are determined by the degree of kidney involvement and its responsiveness to treatment with corticosteroids and other measures. Persons with severe and persistent thrombocytopenia (deficiency of blood platelets) and hemolytic anemia or with central nervous system disease fare poorly compared with those whose illness mainly involves the joints.
There are a number of medications that have been found to be responsible for the induction of a lupuslike disease. Typically, this disease is manifested by the appearance of fever, joint pain, pleurisy, deficiency of white blood cells, and the development of various antinuclear antibodies (antibodies that interact with cell nuclei). The clinical features thus closely resemble those of lupus, with the exception that evidence of kidney involvement is notably rare, and the symptoms generally disappear upon discontinuation of the offending drug. Medications that have had this effect include hydralazine, procainamide, various anticonvulsants, isoniazid, penicillin, and penicillamine. In one study, these or other drugs were found to account for 3 to 12 percent of all the cases identified as lupus. Only a small proportion of persons who receive these drugs present evidence of a lupuslike disease.