Anti tumour necrosis factor - alpha : does it rescue bone loss in inflammatory bowel disease patients?
I. I inflammatory Bowe1 Disease
I. I. I General Overview
Inflammatory bowel disease (IBD) is a group of disorders of the gastrointestinal tract characterized by intestinal inflammation and a chronic relapsing course. IBD has traditionally been categorized as either ulcerative colitis (UC) or Crohn's disease (CD) on the basis of clinical, radiological, endoscopic and histological criteria [I], (Figure 1.1 and Figure 1.2). About 10 % of colitis cases show overlapping features of the two major forms and are designated intermediate colitis [I]. Both UC and CD are commonly characterized by a series of clinical exacerbations and remissions requiring long term use of medications, and frequently necessitating surgical interventions.
Figure 1.1: Endoscopic appearance of Ulcerative colitis  - marked by diffuse,
superficial inflammation of the colonic mucosa, beginning in the rectum and extending proximally to involve any contiguous length of colon.
Figure 1.2: Endoscopic appearance of Crohn's colitis  - marked by transmural nflammation of the colonic mucosa.
see figures in thesis.
Although the etiology of IBD remains to be defined, recent experimental and clinical studies suggests that the initiation and pathogenesis of these diseases are multi-factorial, involving interactions between genetic, environmental and immune factors .
I. I.2 Prevalence and Incidence
IBD is not evenly distributed world-wide. There is a clear tendency to a higher incidence in developed countries compared with less developed countries . North America, the United Kingdom and Scandinavia have the highest rates . In areas in which data are available over a number of years, the incidence of UC has remained relatively constant [S-81. Unlike UC, the incidence of CD has risen progressively since its original description [9-131. In a European study the reported incidence rates for UC and CD in Ireland were 14.8 and 5.9 per 100,000 populations over a two year period 1991-1993 . UC and CD are most commonly diagnosed in late adolescence and early adulthood, but the diagnosis may occur at all ages.