The irritable bowel syndrome (IBS) is the best known of the functional gastrointestinal tract disorders. Many IBS patients have at least one co-morbid somatic complaint and many meet diagnostic criteria for other functional disorders. Patients with IBS and another functional disorder, in comparison with patients with IBS only, have more severe IBS symptoms, a higher rate of psychopathology, greater impairment of quality of life, and more illness-related work absenteeism. Estimates of the prevalence of IBS in patients with fibromyalgia range from 30-35% to as high as 70%. Studies of IBS among patients with chronic fatigue syndrome have reported a prevalence ranging from 35-92%. The prevalence of IBS among patients with chronic fatigue syndrome is reported to be 14%. IBS patients with other co-morbid functional disorders appear to manifest a greater degree of somatization. It has been suggested that the presence of multiple co-morbid disorders may be a marker for psychological influences on etiology. This raises the question of whether the functional syndromes represent the same pathophysiological process, i.e., are the same entity that has been separated into different clinical entities because of medical sub-specialization, or are indeed separate disorders. While the answer to this question awaits further research, it would appear that most functional patients who meet formal diagnostic criteria for more than one functional disorder manifest one disorder clinically more that the others and seek consultation differentially for that set of symptoms.
Keywords: Co-morbidity; Fibromyalgia; Irritable bowel syndrome; Psychopathology.