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Connective tissues are among the most widely distributed and abundant tissues in the body (Volk, 2010). These tissues are involved in many functions among which are providing shape and mechanical support of cells, modulation of cell migration, nutrient transport within and between cells, cell growth and differentiation. The basic components of connective tissue are ground substances, fibrous components and migrating cells (Connective Tissue, 2010). The fibrous component is made up of collagenous, reticular and elastic fibers, which differ markedly in their chemical and physical structures and properties. The most abundant component is collagen which can be found in many cell types. Elastin fiber can be stretched and returned to its original shape; it is the major component of skin. Ground substances are composed of carbohydrates and carbohydrate-protein complexes; the more common ground substances being chondroitin sulfate, and hyaluronic acid. The cells of connective tissues may be the migrating type (macrophages, eisonophils, plasma, mast cells) or stationary like adipocytes and fibrocytes (Connective Tissue, 2010).
Connective tissues are highly diverse but can be categorized to be either loose or dense. The regular dense connective tissues are the tendons and the ligaments. Loose vascular tissue has the synovial membrane which produces synovial fluid which functions as a lubricant for the joints. Cartilage is a connective tissue that has a large amount of ground tissue responsible for its gel-like consistency and flexibility. Other cartilages are made up of hyaline and elastic fibers. Bone and blood are two other kinds of connective tissues. Red blood cells comprise blood tissues while calcium phosphate is an important component of bone tissue (Connective Tissue, 2010).
Types connective tissue disorders/diseases
Connective tissue disorders result when the tissues are damaged and become dysfunctional. There is a wide and diverse range of these diseases, but they can be grouped into three main categories (Connective Tissue Disease, 2010). The first type of connective tissue disorder occurs when there is damage and inflammation when one's own immune system attacks the connective tissues. These diseases can be characterized by an overproduction of antibodies that can be measured in the blood. The second type of connective tissue disorders are due to inherited genetic defects or gene abnormalities. Usually, the inherited disorder also causes tissue abnormalities in other organs like the h eart, lungs, eyes, and bones. Some connective tissue disorders also show general symptoms for the early stage of the disorders, but the symptoms may or not progress to a full stage disease. These disorders fall under the third and general classification of "undifferentiated connective tissue disorder" or UCTD.
The pathophysiology and diagnosis of the autoimmune connective tissue diseases
Although there are many types of autoimmune connective tissue disorders, this paper will only discuss lupus, rheumatoid arthritis and scleroderma. These have a higher prevalence in the population compared to the other diseases. In these diseases, the immune system attacks the connective tissues resulting in inflammation and abnormalities in the blood vessels. The reason for these autoimmune attacks is the subject of many studies, but no coherent theory has been forwarded yet.
Systemic lupus erythematosus
Lupus or SLE is a chronic inflammation of the connective tissues which can affect the skin, joints, lungs, kidneys and other organs of the body (Ginzler, 2008) (Choi & Abueg, 2009). Patients with lupus have arthritis or pain in the joints which could last for weeks. They could also present with rashes (butterfly shaped rash on the cheeks, and other skin areas that are exposed to the sun). General fatigue, sores, loss of hair and seizures. Pregnant women may also experience miscarriage. Other symptoms are heartburn, chest and abdominal pain. Since the symptoms develop gradually, lupus is not detected immediately which can lead to damage of the kidneys, lungs and brain.
There are eleven essential criteria for diagnosing SLE (Tan, et al., 1982) (Gill, Quisel, Rocca, & Walters, 2003). Of the eleven criteria ser, four must be met for a diagnosis of SLE. The primary test is the antinuclear antibody titer (ANA), although it has low predictive value in patients who do not have the usual clinical symptoms. When the ANA points to a positive result in these patients, other antibody tests must be performed to confirm the diagnosis (Gill, Quisel, Rocca, & Walters, 2003).
Rheumatoid arthritis is a chronic disease where immune cells attack and inflame membrane around multiple joints resulting in stiffness, swelling, and pain in the joints (Ruderman & Tambar, 2008). Rheumatoid arthritis is more common in small joints in hands and feet, but it can also affect other larger joints. This pattern is a characteristic of rheumatoid arthritis, although it can also affect other organs aside from the joints. A unique characteristic of the disease is the occurrence of prolonged stiffness in the morning, which is not observed in other arthritis types. Symptoms of rheumatoid arthritis are loss of appetite and energy, presence of low-grade fevers, dry mouth and eyes, and presence of rheumatoid nodules, which are hard lumps, underneath the skin of hands and elbows.
The synovium has been the focus of studies aimed at understanding the pathogenesis and pathophysiology of rheumatoid arthritis. The synovium is the thin lining surrounding the cartilage of the joints and is a major source of nutrients of the cartilage. In normal cells, the lining is 1-3 cells thick while it is 5 - 7 cells thicker in rheumatoid arthiritis (Bathon, 2010). The synovium is where events leading to inflammation occur.
The first theory regarding the pathogenesis of rheumatoid arthritis believes the interaction of T cells with as yet unidentified antigen initiates the inflammatory process and pregression of the disease. This belief is based on the known increased amounts of class II major histocompatability antigens, CD4+ T cells and T cell receptor gene usage synovium, the thin tissue that lines the cartilage in joints (Bathon, 2010). In the second theory, it is believed that macrophages and fibroblasts cause the perpetuation of the inflammation. This is based on the results of studies that show that activated T cells phenotype are relatively absent in chronic rheumatoid arthritis, while there is a proliferation of activated macrophages and fibroblasts. The macrophages produce cytokines IL-1 and TNF activate the fibroblasts. These fibroblasts secrete prostaglandins, proteases and other cytokines (IL-6, IL-8) that promote inflammation, and erode bone and cartilage (Bathon, 2010) (Maini, et al., 1999).
Understanding the pathophysiology and the possible causative elements of rheumatoid arthritis has led to the development of new medications aimed at reducing signals that resultin autoimmune attacks.
Just like lupus, rheumatoid arthritis is difficult to diagnose, especially during the early stages. The initial symptoms are subtle and are similar to those observed for aching joints and muscle stiffness that is normally observed in the morning (Ruderman & Tambar, 2008). Therefore, a skilled rheumatologist is necessary for the correct diagnosis of the clinical symptoms. Physical examination of the joints is necessary. Certain laboratory tests have to be performed. Red blood cell count must be performed, since anemia is common in patients with rheumatoid arthritis. In addition tests for rheumatoid factor, antibodies to citrullinated peptides, and erythrocytes sedimentation rates (Ruderman & Tambar, 2008). Furthermore, in the late stages of the disease, X-rays can be helpful in diagnosing if the disease has progressed. It is important to know that a single test will not confirm a single diagnosis, thus several tests have to be conducted to confirm the condition.
Scleroderma or sclerosis is a rare autoimmune disease that affects the skin characterized by a tightening and thickening of the cells. The activation of immune cells results in the production of scar tissue in skin, small blood vessels and internal organs (Merkel, 2008). For some forms of the disease, scleroderma is not yet curable. There are two types: localized scleroderma, which manifests skin lesions, and systemic scleroderma, which can potentially lead damage to internal organs. Changes in scleroderma are due to increased and accumulated collagen, extending from the skin to other internal organs.
It is still unclear what causes scleroderma, although it is known that it is not infectious and is not inherited from parent to child. Exposure to toxins and some environmental agents is believed to cause the disease but this has to be proven. It is also known that there is tissue damage, inflammation and skin swelling. Blood vessels are also damaged which can cause poor blood flow, gangrene and ulcers. All these result in scarring, and could be life threatening.
Diagnosis of scleroderma is based on physical and clinical examinations. Aside from thickening of the skin, blood vessels may be dilated in the face, and other parts of the body. Calcium deposits can also be found in skin and other organs. Laboratory tests for auto-antibodies are also used, but results may not be conclusive.
Mixed connective tissue disease
The mixed connective-tissue disease (MCTD) features the existence and overlapping of various connective-tissue diseases such as systemic lupus erythematosus, sclerosis, polymyositis and, occasionally, Sjögren syndrome. MTCD is usually milder than the other diseases and is usually considered and intermediate stage progressing to either systemic lupus erythematosus or scleroderma.