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Statistical co-morbidity of IBS and depression
If you have irritable bowel syndrome and also suffer from depression, you are not alone. Rates of co-morbidity for depression in IBS sufferers is reportedly as high as 40%,1 or 94% with psychiatric disorders including major depression.2 On the face of it the connection might seem a touch obvious: the natural assumption might be that, well, IBS is a very depressing condition! Irritable bowel syndrome symptoms include pain/discomfort (improving with defecation), change of frequency and form of stool3 and extra-intestinal symptoms11 and may be IBS-D (diarrhoea predominant), IBS-C (constipation predominant) or IBS-A (alternating).1
Is it common sense to assume that depression may follow upon such a disagreeable daily experience, as a simple matter of direct causation? One might ask instead if depression leads to IBS. Depression has after all been associated with a host of somatic symptoms1,4 such as fibromyalgia and fatigue. Could depression feature on the list of possible irritable bowel syndrome causes?
Lackner et al's 2004 study suggests that the pain perception of depressed individuals may be distorted. Their subjective evaluation of the severity of their gastrointestinal discomforts seems to be heightened, although the researchers do not claim all such symptoms to be psychogenic.5
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Is there a genetic factor involved in development of IBS?
One may hypothesize that, rather than a direct causal relationship in either direction, both IBS and depression flow from a common cause. What mechanism or pathway might produce this result? Could there be a possible genetic causation of co-morbidity of IBS and chronic psychological disorders such as generalized anxiety disorder or depression?
The monozygotic/dizygotic twins study by Wojczynski et al6 concludes that genetic factors cannot explain co-morbidity of major depression and irritable bowel syndrome. On the other hand the role of the serotonin transporter in IBS-C has been examined: as well as being a 'player' in depression via selective serotonin reuptake inhibitors, transporter polymorphisms may be implicated in IBS.8
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How complex is the pathogenesis of IBS and depression?
One might hypothesize that a direct causal chain is not the only option: might environmental and genetic factors interplay as IBS causes to produce both depressive and IBS symptoms? Of course if the relationship between irritable bowel syndrome and depression was causal this might also apply: could an interplay between the two exist producing a downward spiral via shared mechanisms and pathways?2,6
In their 2007 study Wojczynski et al concluded that IBS may be a result of pathophysiological processes in major depression – or vice versa.6 Whitehead et al however dispute their assertions of pathophysiological causal links between IBS and depression, on the basis that such co-morbidity is not invariable nor is it specific to depression but is also linked to fibromyalgia and fatigue.5 A 2004 study by Tache et al suggests a shared signalling pathway for generalized anxiety disorder and IBS-D through corticotropin signalling factor and related ligands: might each condition escalate the other? This study also reviews the literature with implications that environmental factors such as stressful events, which might be expected to produce anxiety or depression, may also aggravate IBS symptoms.9
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New treatment possibilities for psychological disorders and irritable bowel syndrome?
If irritable bowel syndrome and psychological problems do share determinants, could they be treated via similar methods or at least attacked via the same pathways? In a study in 2003 the SSRI paroxetine was found to improve well-being in a treated group of IBS sufferers as opposed to those receiving a placebo.10 Tache et al's study of transmitter molecules implicated in anxiety disorders found that perception of IBS pain and distension was heightened by the ligands used: might treatments for anxiety via this pathway also assist IBS?9
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IBS and depression co-morbidity: conclusion
There is statistical evidence of co-morbidity, and studies to suggest that depression (and other mental conditions) and IBS may be interrelated to some degree in terms of causation and possibly treatment. As more research is done into connections between the two, it is less and less surprising to find instances of co-morbidity of irritable bowel syndrome and psychological disorders such as depression and GAD.
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1 Cole, Alexander J., Kenneth J. Rothman, Howard J. Cabral, Yuqing Zhang, and Francis A. Farraye. "Migraine, fibromyalgia, and depression among people with IBS: a prevalence study." BMC Gastroenterology 6 (September 2006): 26+.
2 Whitehead , W.E. “Systematic review of the comorbidity of irritable bowel syndrome with other disorders: what are the causes and implications? “ Gastroenterology 1 (April 2002): 122(4): 1140-56
3 Rome Foundation, Inc. “Rome III Diagnostic Criteria for Functional Gastrointestinal Disorders” Rome III Disorders and Criteria. 2006. Rome III Disorders and Criteria. <http://www.romecriteria.org/assets/pdf/19_RomeIII_apA_885-898.pdf>
4 Haug, Tone Tangen, MD, PhD, Arnstein Mykletun, MA and Alv. A. Dahl, MD, PhD. “The Association Between Anxiety, Depression, and Somatic Symptoms in a Large Population: The HUNT-II Study.” Psychosomatic Medicine 66:845-851 (2004)
5 Lackner, J.M., PsyD, Brian M. Quigley, PhD and Edward B. Blanchard, PhD . “Depression and Abdominal Pain in IBS Patients: The Mediating Role of Catastrophizing”. Psychosomatic Medicine 66:435-441 (2004)
6 Wojczynski, K. Mary, North, E. Kari, Pedersen, L. Nancy, Sullivan, and F. Patrick. "Irritable Bowel Syndrome: A Co-Twin Control Analysis." The American Journal of Gastroenterology 102 (October 2007): 2220-2229.
7 Whitehead and E. William. "Twin Studies Used to Prove That the Comorbidity of Major Depressive Disorder With IBS Is NOT Influenced by Heredity." The American Journal of Gastroenterology 102 (October 2007): 2230-2231.
8 Kim HJ, Camilleri M, Carlson PJ, Cremonini F, Ferber I, Stephens D, McKinzie S, Zinsmeister AR, Urrutia R. “Association of distinct alpha(2) adrenoceptor and serotonin transporter polymorphisms with constipation and somatic symptoms in functional gastrointestinal disorders.” Gut. 2004 Jun;53(6):829-37.
9 Tache, Y., Martinez, V., Wang, L., Million, M. “CRF1 receptor signaling pathways are involved in stress-related alterations of colonic function and viscerosensitivity: implications for irritable bowel syndrome.” British journal of pharmacology 2004;141(8):1321-1330
10 Tabas G, Beaves M, Wang J, Friday P, Mardini H, Arnold G. “Paroxetine to treat irritable bowel syndrome not responding to high-fiber diet: a double-blind, placebo-controlled trial.” Am J Gastroenterol 1 (May 2004). 99(5): 914-20
11 Gunnarsson, J. and Magnus Simrén “Efficient diagnosis of suspected functional bowel disorders”. Nature Clinical Practice Gastroenterology & Hepatology (2008) 5, 498-507