Functional Constipation and Functional Diarrhea

Changes in bowel habit is often associated with dietary factors or acute diseases. Less commonly, underlying chronic disease or the use of chronic medication can impact on the frequency of bowel movements with or without an associated change in the stool consistency and volume. Diarrhea is defined as the passage of more than 200ml/200g of stool, usually loose and watery, in a 24 hour period and/or in more than 3 bowel movements within a day. Constipation is defined as the passing of hard stool, with straining and pain and/or less than 3 bowel movements within a week. Despite these definitions, the presentation of these symptoms can vary among individuals. While acute episodes can be explained by infections, dietary and lifestyle factors or iatrogenic causes, there are instances where persistent or recurrent episodes of disordered bowel movement occurs for no known reason. This means that it is neither due to some underlying disease or identifiable physiological factors. In these cases, the change in bowel habit may be associated with a functional bowel disorder.

Difference with Idiopathic Constipation and Diarrhea

There are several functional bowel disorders but those associated with changes in bowel habit include irritable bowel syndrome (IBS), functional constipation and functional diarrhea. While irritable bowel syndrome is characterized by changes in bowel habit, either constipation or diarrhea, abdominal discomfort/pain is also a prominent feature. In the absence of this abdominal discomfort/pain, the change in bowel habit may be considered to be either functional constipation or functional diarrhea.

Idiopathic constipation or diarrhea on the hand indicates a pathological (disease) process although the exact cause cannot be identified. In the absence of known physiological factors and if there is no biochemical markers or symptoms to indicate any pathology, chronic diarrhea should be considered a functional in nature, whether functional diarrhea or irritable bowel syndrome.

What is functional constipation?

Functional constipation is the persistent difficulty with passing stool characterized by straining during defecation, infrequent bowel movements and/or a feeling of incomplete evacuation after a bowel movement. It is not associated with abdominal pain or discomfort as in IBS and there is no underlying pathological or physiological reason for these symptoms. Functional constipation is diagnosed by the presence of two or more of the following criteria :

  • Lumpy or hard stools in at least 1 out of 4 bowel movements.
  • Straining during at least 1 out of 4 bowel movements.
  • Sensation of incomplete evacuation following at least 1 out of 4 bowel movements.
  • Sensation of anorectal obstruction in at least 1 out of 4 bowel movements.
  • Less than 3 bowel movements in a week.
  • Manual intervention to facilitate defecation in at least 1 out of 4 bowel movements.

These symptoms should have been present within the last 3 months and have started 6 months or more before diagnosis.

Causes of Functional Constipation

The exact cause of functional constipation is unknown. It may be associated with a slower than normal bowel transit time as a result of dysfunctional gastrointestinal motility. Increased time within the tract may account for the hard and dry stools. Anorectal dyssynergia is a dysfunction involving the muscles associated with defecation particularly those controlling the movement of feces into the rectum, external anal sphincter and/or pelvic floor muscles. However, a person can have normal bowel transit time indicating normal gastrointestinal motility with normal anorectal function and still have functional constipation. It is believed that a psychosomatic component may also be involved as it is more likely to occur in a person undergoing psychological stress and depression. A link with hormonal levels have not been conclusively proven although constipation in general is more common in women.

Treatment of Functional Constipation

The approach to treating and managing functional constipation is not significantly different from treating constipation due to other causes. This includes :

  • Increasing fiber intake, particularly through dietary modification by consuming more fruits and vegetables. Fiber supplements may also be useful.
  • Increasing daily water intake.
  • Exercise regularly.
  • Laxatives may be used periodically particularly with bowel retraining.
  • Serotonin agonist like tegaserod may also be helpful in stimulating intestinal motility.

Despite these measures, which at times can be minimally effective, the constipation may not resolve. Since no distinct causative factor can be found, it is difficult to treat the underlying cause or remove the offending agent.

What is functional diarrhea?

Functional diarrhea is continuous or recurrent episodes of passing loose and watery stool often associated with frequent bowel movements or urgency to defecate. This is irrespective of the number of bowel movementsor volume of stool in a 24 hour period. Abdominal discomfort or pain is clearly absent. There is no underlying pathological or physiological reason for the diarrhea. It corresponds to type 6 and type 7 stool consistency as indicated under the Bristol Stool Chart (refer to the chart under loose stool). Frequency of bowel movement and urgency to defecate associated with normal solid stools is considered as pseudodiarrhea. Functional diarrhea is diagnosed by the presence of :

  • Loose, watery / mushy stools in at least 3 our of 4 bowel movements.

These symptoms should have been present within the last 3 months and have started 6 months or more before diagnosis.

Causes of Functional Diarrhea

As with other functional bowel disorders, the exact cause of functional diarrhea is unknown. It is believed that the diarrhea is associated with rapid gastrointestinal motility leading to a faster than normal bowel transit time. The reduced time period in which food is within the bowel may hamper digestion and nutrient absorption. It is clear that water absorption is significantly hampered hence the loose watery stools. The urgency to defecate and at times loss of bowel control (bowel incontinence) may be a result of distension of the distal bowels and the anus making contact with water. The role of psychological stress has not been investigated thoroughly. The effect of certain foods like dairy and stimulant use particularly nicotine and caffeine has also not been conclusively corroborated but may be helpful.

Treatment of Functional Diarrhea

The treatment options are limited since the exact cause cannot be identified. Dietary modification that can be helpful varies among individuals but may include :

  • Discontinuing the intake of foods which are known irritants like dairy, artificial sweeteners and caffeinated drinks. Any other foods which may be a factor in individual cases should also be avoided.
  • High fiber intake may be helpful in improving the consistency of stool but can be an irritant for some patients.

Counseling and stress management is also advisable for patients experiencing psychological stress.

Medication that may be of use is limited. Antidiarrheal agents like loperamide may be a short term solution but should not be used indefinitely.

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