Chronic Constipation

Constipation is defined by the Rome IV criteria rather than by frequency alone: fewer than three spontaneous bowel movements a week, straining, hard or lumpy stools, a sense of incomplete evacuation, or the need for manual manoeuvres, in at least a quarter of bowel movements over three months. Stool consistency, best described using the Bristol Stool Form Scale, is often a more useful measure than count. Most chronic constipation is functional, meaning no structural cause is found. Within that, it is worth distinguishing normal-transit constipation, slow-transit constipation, and defecatory disorders such as pelvic floor dyssynergia — the last of these responds to biofeedback rather than to laxatives, and is frequently missed. Prevalence is around 14% globally and rises with age. It is roughly twice as common in women and disproportionately affects older adults, in whom medication burden, reduced mobility and lower fluid intake compound. Treatment escalates in a predictable order: fibre and fluid, then an osmotic laxative such as polyethylene glycol or magnesium, then a stimulant laxative for rescue, then prescription secretagogues. Magnesium oxide and citrate work well here precisely because they are poorly absorbed and hold water in the bowel — the same property that makes them a poor choice for correcting magnesium deficiency.

• •Fewer than three bowel movements per week
• •Hard, dry or lumpy stools
• •Straining to pass stool
• •Sensation of incomplete evacuation
• •Sensation of anorectal blockage
• •Need for manual manoeuvres to pass stool
• •Abdominal bloating and discomfort
• •Reduced appetite

• •Low dietary fibre intake
• •Inadequate fluid intake
• •Physical inactivity
• •Ignoring or delaying the urge to defecate
• •Opioid analgesics
• •Iron supplements, calcium channel blockers, anticholinergics and some antidepressants
• •Hypothyroidism
• •Diabetes and other causes of autonomic neuropathy
• •Pelvic floor dyssynergia
• •Irritable bowel syndrome, constipation-predominant
• •Pregnancy

Functional constipation reflects some combination of slow colonic transit, impaired rectal sensation, and disordered coordination of the pelvic floor during defecation. The last is important because it does not respond to laxatives: in pelvic floor dyssynergia the pelvic floor muscles contract instead of relaxing during straining, and the treatment is anorectal biofeedback. Secondary causes — medication effects, hypothyroidism, diabetes and, rarely, obstruction — should be excluded before settling on a functional label.