The Pathophysiology and Mechanisms of Constipation, IBS, and Diverticulosis in Older People
Abstract & Commentary
Synopsis: Constipation and diverticulosis increase with aging, while the prevalence of irritable bowel syndrome remains the same as in younger adults. Aging alone is a less important contributor to constipation than related factors such as drugs, immobilization, and diet.
Source: Camilleri M, et al. J Am Geriatr Soc 2000;48: 1142-1150.
English language journal articles and reviews from the last 24 years were evaluated to determine current understanding of the pathophysiology and mechanisms of colonic motor dysfunction which contribute to constipation, irritable bowel syndrome (IBS), and diverticulosis in older persons. Constipation had a commonly reported prevalence of 24%, which was significantly higher than that reported in younger persons aged 30-64 years. IBS was less common at 11% and fairly similar across all ages. Some studies distinguished subgroups of chronic constipation: 24.4% functional (infrequent of incomplete defecation) vs. 20.5% rectal outlet delay (straining and need to facilitate defecation with digitation). The latter was more common in women, and the rates of functional constipation increased with advancing age.
Medications, particularly nonsteroidal anti-inflammatory drugs, were significant risk factors in surveys for both the functional and rectal outlet delay types of constipation. These disorders also had a major effect when quality of life surveys were conducted, being associated with the poorest ratings of physical function.
Diverticulosis also increases with advancing age (found in postmortems in 56% of persons > 70 years), and seems to have different locations in different countries. In the United States and other western countries, diverticulosis occurs in the sigmoid and left colon, while in Japan it is more often found on the right side and at younger ages. However, increasing trends to the left are being seen in Japan, suggesting environmental and dietary effects. There is speculation that this condition will decrease in the future due to the increase of dietary fiber in the general population.
Although research into gastrointestinal (GI) physiology for persons older than 65 years is limited, it is known that the ultrastructure of the colonic wall changes with age, with collagens in the submucosal network becoming smaller and more tightly packed. While it is hypothesized that differences in propulsion through defects in the colonic wall may produce diverticula, this had not been proven. The ascending and transverse colon are often longer and pendulous in older persons, and some studies suggest delayed transit time in the proximal colon for persons with constipation, although overall transit time was not always affected. Studies which do document prolonged transit time suggest that immobilization and medication effects may be more responsible than aging alone.
Neurotransmitter studies in aging animals show a reduced number of neurons with aging, and in humans the decrease seems to be in inhibitory neurons that could contribute to colonic spasm or the lack of relaxation found in IBS, constipation, and diverticulosis. Release of the neurotransmitters crucial to neuromuscular activation is calcium-dependent, and age-related changes in calcium signaling have been reported in other areas of the nervous system. It is also speculated that nerve growth factors (neurotrophins) may be depleted and could cause neuronal dysfunction and cell death. Limited studies with healthy patients using recombinant human brain-derived neurotrophins increased stool frequency and accelerated colonic transit.
Pelvic floor and sphincter dysfunctions may result from aging changes, particularly decreased anal pressures and lower rectal volume required to cause the urge to defecate. In older women an insufficient opening of the rectoanal angle compared to younger women contributed to failure of rectal evacuation; this was attributed to laxity in the support of the perineum.
Current treatments for constipation may be directed to the predominant dysfunction, when known: evacuation disorders require regular use of suppositories or enemas to avoid impaction, while biofeedback and relaxation techniques are most useful for spastic pelvic floor disorders rather than perineal laxity. For both IBS and constipation, the recommended approach is adequate hydration, increased mobility, fiber supplementation (15-25 g/d), and an osmotic laxative or stool softener.
Comment by Mary Elina Ferris, MD
Considering the impending explosion of the population older than age 75 and the widespread prevalence of functional GI complaints in the elderly, it behooves us to devote more attention and basic research to the physiologic mechanisms causing these problems. The discomfort associated with these GI complaints affects both patient quality of life and practitioner frustration levels when dealing with inadequate treatments. This seemingly straightforward problem actually has a complex and interrelated set of possible etiologies, and accounts for many medical visits.
While new insights into possible colonic neural loss or injury as causes for aging dysfunction are intriguing research topics that may lead to specific treatments, even the extensive literature search in this study showed limited evidence for these causes. Attention to the less glamorous etiologies of adequate hydration, diet, and mobility, along with evaluation of medication effects, will continue at present to improve the bowel function of our older patients more positively than any new pharmaceuticals to replace neurotransmitter levels. We can only hope that the research dollars that will be allocated to the neuromuscular etiologies will be matched by practical evaluations of how to more effectively use existing knowledge to help improve the quality of life for our older patients.
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