PR Bleeding

PR bleeding can vary from a smear on toilet paper through to severe haemorrhage. It may be the first presenting symptom of colorectal cancer.

Differential diagnosis

Common causes: haemorrhoids, polyps, colorectal cancer (CRC), diverticular disease, perianal excoriation, anal fissure.

Must not miss: CRC, ischaemic colitis.

Red flags: age >50 years; change of bowel habit; weight loss; weakness/fatigue; brisk bleeding; constipation; family history of CRC; blood mixed with (rather than on) stool.

Pitfall — not every bleed noticed “down below” is rectal. A case report of an elderly man presenting with concern about blood stains in his underwear turned out, on closer examination, to be bleeding from angiokeratoma of Fordyce (benign vascular papules on the scrotum) rather than the rectum — his PR exam was unremarkable, and the true source was only found once the perianal/genital skin itself was inspected. Always examine the perianal skin and external genitalia, not just the rectum, before attributing blood in the underwear to a PR bleeding cause.

History

Historical features usually differentiate between the common causes:

• Bright red blood on toilet paper, separate from faeces — haemorrhoids.
• Pain associated with passing stool — anal fissure.
• Tenesmus — concerning for a rectal/anal mass; also occurs in IBS, but shouldn’t be associated with bleeding in that case.
• Blood/mucus mixed with faeces — polyps, CRC, inflammatory bowel disease, ischaemic colitis, proctitis.
• Just blood mixed with faeces — CRC, polyps.

Examination

Inspection of the perianal area: look for external haemorrhoids, fissures, sentinel skin tags.

PR examination: feel for masses (haemorrhoids usually cannot be felt); significant pain suggests a fissure.

Proctoscopy: look for haemorrhoids (purplish bulges projecting into the anal canal) and masses.

Treat as per the underlying condition (see the relevant condition page). For an anal fissure specifically, topical glyceryl trinitrate (GTN) is marginally but significantly better than placebo in healing anal fissure, though late recurrence of fissure is common once treatment stops; topical calcium-channel blockers or botulinum toxin injection are similarly effective alternatives with fewer side effects (GTN’s main drawback is headache).