**1. Introduction**

Rheumatology is a branch of science dealing with the different conditions that affect musculoskeletal tissues such as joints, bones, cartilage, tendons, ligament, and muscles. Rheumatism refers to various painful conditions that affect these tissues. Rheumatic diseases are those groups of diseases showing pain followed by reduction in the range of motion and function of musculoskeletal tissues. Arthritis is also one type of rheumatic disease referring to joint inflammation whether for joint pain, stiffness, inflammation, or joints damage. Most common types of rheumatic disease are rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) (**Figure 1**). The autoimmune diseases (such as RA, SLE, multiple sclerosis, and inflammatory bowel) have complex pathogenesis and multiple etiologies [1]. Studies have reviewed the role of various factors including genetic factors, epigenetic regulation, and environmental factors (such as cigarette smoking, crystalline silica, Epstein-Barr virus and reproductive hormones) in the pathogenesis of these autoimmune diseases [1]. There are many evidences showed that autoimmune diseases are multigenetic and their identification is associated with various types of genes [2]. There are a group of genes which induced the expression of proteins involved in various key pathophysiological pathways such as formation and clearance of immune complexes or apoptotic material, control of innate and adaptive immunity, production of immunological molecules like cytokines, chemokines, and adhesion molecules [3, 4]. Autoimmune patients have a great diversity in their genetic background and the nature of genes decides what kind of responsiveness is required to change the state of immune system [5]. There are various environmental factors that play an important role in these autoimmune diseases. These include infectious agents, ultraviolet (UV) light, and chemical or other compounds modifying immunological responses like environmental pollutants, drugs, or other behavioral habits such as smoking or diet [6, 7].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

between the potential risk of SLE and alcohol consumption because the habit of smoking and alcohol often coexist, which interferes with the exact interpretation of the coexisting risk of development of SLE and alcohol habit [17]. One of the earlier studies has shown that neither past nor current alcohol consumption was associated with the development of SLE [18]. In an Internet-based study, it was found that current drinking habits are inversely associated with the development of SLE [19]. Certain medications are also known to induce lupus-like symptoms. Drug such as procainamide, which is an anti-arrhythmic drug, might induce lupus-like syndrome by acting as an inhibitor for DNA methyltransferase in human T cell lines [20]. Anti-TNF has been used in the treatment of inflammatory arthritis and is known to cause anti-TNF-induced lupus [21]. In addition, recent data suggest the role of estrogen and their

Introductory Chapter: Introduction to Rheumatology http://dx.doi.org/10.5772/intechopen.81595 5

Rheumatoid arthritis (RA) is a chronic inflammatory disorder in which inflammatory response develops especially in synovial joints. In this disease, the immune system mistakenly attacks our own body's tissues. It affects mainly the lining of the joints and results in painful swelling of the joints that in turn results in bone erosion and causes joint deformity. The inflammation associated with the joints can damage the other parts of the body as well. There are various disorders associated with RA [27]. These include depression, fatigue, malaise, and anorexia. In addition to that, there are various complications including cardiovascular and hematologic complications, neurological problems, respiratory system disorders, and various other complications associated with RA. RA is found worldwide and affects nearly about 1% of the world population [28]. Women are more likely to have this disease, and it generally occurs at older age. Rheumatoid arthritis generally occurs at an age in between 30 and 50 years of age and its incidence varies among different populations. The actual cause of this disease is unknown but it is assumed that it probably occurs if a genetically susceptible host gets exposed to an environmental antigen [29]. This might generate immune response leading to the formation of various types of immune complexes, which generate inflammation in the joints. Recently, one study showed how inflammation occurs in joints of these rheumatoid arthritis patients [30]. Synovial cells produced high concentration of 16α-hydroxyestrone in rheumatoid arthritis patients. Despite normal concentration of 16α-hydroxyestrone in serum and urine, there is an elevated 16α-hydroxyestrone found in the synovial tissues, where activated immune cells are present. Therefore, 16α-hydroxyestrone combined with histone resulted in the formation of 16α-hydroxyestrone-histone adduct that might generate autoantibodies against this antigen. As a result, these autoantibodies trigger inflammation in the joints of RA patients [30]. Some studies also showed that viral or bacterial infections could act as potential environmental culprits to cause RA. Immunization with type II collagen also caused RA in experimental animals. Some patients of RA have shown that autoantibodies directed against heat shock proteins might show cross-reactivity with the bacterial antigen. There are numerous signs and symptoms associated with RA [31]. The most commonly affected joints in RA include fingers, feet, wrists, elbows, ankles, and knees. Shoulder, hip, and cervical spines are among those joints

metabolites in the pathogenesis of lupus [22–26].

**3. Rheumatoid arthritis (RA)**

**Figure 1.** Different terms used in rheumatology.
