Red flags
- New constipation >50 years with weight loss, PR bleeding, iron-deficiency anaemia - colorectal cancer until excluded
- Absolute constipation with distension/vomiting - obstruction
- Faecal incontinence/overflow in the context of impaction
- New neurological signs (saddle anaesthesia, urinary retention) - cauda equina
- Severe abdominal pain out of proportion - toxic megacolon, ischaemia
Differential by mechanism
Functional/lifestyle
- Low fibre/fluid intake, immobility, ignoring urge
Drug-induced (common, always check first)
- Opioids, anticholinergics, iron, calcium channel blockers, 5-HT3 antagonists, aluminium antacids
Metabolic/endocrine
- Hypothyroidism, hypercalcaemia, hypokalaemia, diabetes (autonomic neuropathy)
Structural/obstructive
- Colorectal cancer, strictures (diverticular, IBD), volvulus, external compression
Neurological
- Parkinson's disease, spinal cord lesion, cauda equina, autonomic neuropathy
Functional GI disorder
- IBS-C, slow transit constipation, pelvic floor dyssynergia
Focused history
- Change from usual bowel habit and duration, stool form (Bristol stool chart)
- Associated alarm features - weight loss, bleeding, family history of colorectal cancer
- Full medication review
- Diet, fluid, mobility, toileting habits
Focused examination
- Abdominal distension, mass, tenderness
- PR exam - impaction, mass, tone, blood
- Neurological exam if cord/cauda equina suspected
Investigation strategy
- Bloods if alarm features/systemic illness: FBE, TFT, calcium, glucose
- Abdominal X-ray if impaction/obstruction suspected
- Colonoscopy if alarm features present or age-appropriate screening overdue
- Anorectal physiology/defecating proctography for refractory pelvic floor dyssynergia
Management
1. Treat the cause
- Deprescribe/adjust causative drugs where feasible (co-prescribe laxative if opioid cannot be stopped)
- Correct metabolic derangement
2. Stepwise laxative therapy
- Osmotic laxative first-line (macrogol/PEG) - preferred over stimulants for chronic use
- Add stimulant laxative (senna, bisacodyl) if inadequate response
- Bulking agents (psyllium) - useful in simple low-fibre constipation but avoid in opioid-induced or slow-transit constipation (can worsen if fluid intake inadequate)
- PAMORAs (methylnaltrexone, naloxegol) for opioid-induced constipation refractory to standard measures
3. Refractory/functional
- Pelvic floor biofeedback for dyssynergia
- Prucalopride (5-HT4 agonist) for chronic idiopathic constipation refractory to standard laxatives
- Surgical options rarely, for confirmed slow transit unresponsive to all medical therapy
Traps
- New constipation with alarm features in an older adult must not be treated symptomatically without colonoscopy
- Opioid-induced constipation does not respond to bulking agents and does not develop tolerance - needs ongoing stimulant/osmotic laxative or a PAMORA
- Overflow diarrhoea from impaction is easily mistaken for infective diarrhoea, prompting the wrong treatment
- Cauda equina is a surgical emergency masquerading as "just constipation" if urinary retention/saddle anaesthesia are missed
Talk track
- "New bowel habit change over 50 with any alarm feature gets a colonoscopy, not just a laxative."
- "For opioid-induced constipation I reach for a stimulant or PAMORA, not a bulking agent."
8 of 8 sections written · drafted 2026-09-13