Differential Diagnosis

Common Diagnoses

  • Diet and Lifestyle (Inadequate Fibre and Ignoring the Urge to Defecate)
  • Inactivity (Especially in the Elderly)
  • Irritable Bowel Syndrome
  • Drugs, e.g. Opiates, Iron, Aluminium Hydroxide
  • Abscess
  • Fissure
  • Florid Warts
  • Haemorrhoids

Occasional Diagnoses

Rare Diagnoses

  • Pressure from Extracolonic Pelvic Masses
  • Acute Bowel Obstruction (Various Causes)
  • Hypercalcaemia
  • Crohn’s Disease with Stricture
  • Infants and Children: Behavioural (‘Stool Holding’), Hirschsprung’s Disease

Ready Reckoner

Key distinguishing features of the most common diagnoses

Diet and LifestyleInactivity IBSPerianal ConditionsDrugs
Likely in ElderlyYesYesNo PossibleYes
‘Overflow’ Diarrhoea PossibleYesNo Possible Possible
Mucus PRNoNo Possible PossibleNo
Short HistoryNoNo PossibleYes Possible
PR Exam Very PainfulNoNoNoYesNo

Possible Investigations

Likely:None; if suspicion of significant underlying bowel pathology, then FBC, FIT, hospitalbased lower GI investigations.

Possible:Urinalysis, thyroid function tests (TFT).

Small Print:Plain abdominal X-ray, serum calcium, ultrasound, CT scan, biopsy.

  • Urinalysis: Specific gravity high if inadequate fluid intake.
  • FBC: May reveal iron deficiency anaemia if underlying carcinoma.
  • FIT: A useful colorectal cancer ‘rule out’ test in patients at low risk. Also commonly required now when arranging a two-week referral to help secondary care stratify urgency of investigation.
  • TFT and serum calcium: Will reveal hypothyroidism or hypercalcaemia.
  • Plain abdominal X-ray: May reveal megacolon full of faeces; erect and supine views will show obstruction.
  • Hospital-based lower GI investigations: May reveal carcinoma or diverticular disease.
  • Ultrasound/CT scan: May be helpful if a pelvic mass is present.
  • Biopsy: Of suspicious lesions or to confirm Hirschsprung’s disease.

Top Tips

  • Clarify what patients mean by constipation – they often use the term inaccurately (e.g. in reference to a perfectly ‘normal’ bowel habit or to describe another symptom such as tenesmus).
  • The longer the history, the less likely there is to be any underlying or remediable cause.
  • Check the medication history (including over-the-counter treatment) – just about any medication can alter the bowel habit.
  • Look at the patient – your immediate impression may give important clues to the underlying diagnosis (e.g. hypothyroidism or weight loss in malignancy).
  • In children with constipation, continue treatment for weeks or even months to achieve easy and pain-free bowel movements. Reassure parents that the use of laxatives does not lead to a ‘lazy bowel’ and that the constipation is not a sign of a ‘blockage’.

Red Flags

  • Constipation alone in the elderly is rarely caused by sinister pathology – but if it is accompanied by other significant symptoms, such as weight loss, rectal bleeding or mucus, or diarrhoea, carcinoma is likely.
  • Beware of attributing abdominal pain to constipation – the true diagnosis might be intestinal obstruction. Visible peristalsis with audible borborygmi is never due to simple constipation.
  • Cases of Hirschsprung’s disease can present ‘late’ – consider the diagnosis in a child with chronic constipation, a persistently swollen abdomen and an empty rectum.
  • Beware of assuming that known pathology (such as diverticular disease or IBS) in an individual is the cause of constipation. If the patient has presented with constipation, then there may have been a significant change in the pattern or the nature of the symptoms.

Published: 1st August 2022 Updated: 10th April 2024

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