Chapter 09 — Perianal Crohn’s Disease and Inflammatory Bowel Disease

Purpose: perianal disease is often the first sign of Crohn’s disease — recognise it before anyone divides a sphincter, and manage it as a combined medical–surgical condition.

🎨 INFOGRAPHIC / VISUAL BLUEPRINT — CHAPTER 09

• Chapter colour palette: Olive Green (#3F6212) header bar, Pale Lime (#F7FEE7) panels, Forest Black (#1A2E05) text.
• Hero graphic: A “two-front” illustration: the inflamed bowel on one side (treated with a biologic infusion) and the perineum on the other (lateral fissures, oedematous tags, two fistula openings with a loose seton) — joined by a handshake between gastroenterologist and colorectal surgeon.
• Icon set: Flaming intestine, calprotectin tube, MRI scanner, loose seton loop, biologic vial, weighing scale, crossed-out scalpel over the sphincter, handshake.
• Bedside aphorism banner: “In Crohn’s disease, drain the pus and protect the sphincter — let medicine heal the fistula.”

1. Perianal Manifestations of Crohn’s Disease

Perianal disease affects a substantial proportion of people with Crohn’s disease over time (perianal fistulas alone in up to about one-third) and may precede intestinal symptoms by months or years [C].

Table 9.1 — Perianal manifestations

2. Idiopathic Versus Crohn’s-Associated Perianal Disease

Table 9.2 — Distinguishing features

3. The “Suspect Crohn’s” Checklist

Two or more items — or any one strong item (complex fistula, recurrent abscess, lateral or multiple fissures with systemic symptoms) — should trigger an IBD work-up and urgent referral before any sphincter-dividing procedure.

4. Investigations

Table 9.3 — Work-up for suspected perianal Crohn’s disease

5. Why Sphincter-Dividing Surgery Is Dangerous in Active Crohn’s Disease

• Wounds heal poorly in inflamed tissue and can become chronic, painful ulcers.

• Continence reserve is already reduced: diarrhoea, urgency, and a stiff, inflamed rectum mean that losing even a small amount of sphincter can cause incontinence.

• Disease is recurrent and multifocal — further operations are likely, and each one costs more muscle.

• Uncontrolled perianal sepsis and repeated surgery can end in a permanent stoma or proctectomy.

• Fistulotomy is reserved for selected simple, low fistulas in patients without active proctitis, decided by a colorectal surgeon (ASCRS 2020) [C]. Haemorrhoid procedures are deferred until remission (AGA 2026) [C].

6. Combined Medical–Surgical Management

Table 9.4 — Treatment principles

Algorithm 9.1 — Perianal disease with possible Crohn’s disease

[PERIANAL PROBLEM: FISSURE, TAG, ABSCESS, OR FISTULA]
|
+-- ANY "SUSPECT CROHN'S" FEATURE? (off-midline/multiple
|   fissures, oedematous tags, recurrent or complex fistula,
|   diarrhoea, weight loss, anaemia, raised CRP, EIMs)
|     -> NO: manage as idiopathic disease (Chapters 04-05)
|     -> YES: treat as possible Crohn's -> NO sphincter
|        division; bloods + calprotectin + stool tests +
|        STI/HIV tests; urgent GI and colorectal referral
|
+-- ABSCESS or sepsis present?
|     -> RED (SAME-DAY): drain; loose seton if a fistula
|        is found; biopsy; cultures
|        Drain BEFORE starting or escalating biologics
|
+-- Fistula with no undrained sepsis
|     -> YELLOW: pelvic MRI -> EUA (+/- seton, biopsy)
|        -> combined GI-colorectal plan: anti-TNF
|           (infliximab first choice) +/- immunomodulator;
|           antibiotics as adjunct only
|        -> remission and no proctitis -> consider repair
|
+-- Known Crohn's with NEW pain, mass, or change in an old
    fistula -> exclude abscess AND malignancy (MRI, EUA,
    biopsy)

7. Dangerous Mimics

Table 9.5 — Conditions that mimic (or coexist with) perianal Crohn’s disease

8. Role-Targeted Action Boxes

🚑 ER DOCTOR ACTION BOX

• Drain the abscess; do not lay open fistulas. Document the number and position of external openings and request colorectal follow-up.
• Patients on biologics, steroids, or immunomodulators may not mount a fever — examine carefully and lower your threshold for imaging and surgical review.
• Avoid starting systemic steroids for a “flare” until perianal sepsis has been excluded. Send stool for C. difficile in every flare.

🩺 FAMILY MEDICINE / GP CLINIC BOX

• Run the “suspect Crohn’s” checklist for every patient with a recurrent abscess, atypical fissure, or oedematous tags.
• Check faecal calprotectin, bloods, and stool tests, and refer urgently to gastroenterology and colorectal surgery.
• Support smoking cessation — smoking worsens the course of Crohn’s disease [S].
• Update vaccinations early, before immunosuppression begins; avoid live vaccines once immunosuppressed.

🏥 ER & WARD NURSE CARE AND SBAR BOX

• Seton care: keep the area clean with water; some discharge is expected; never pull or tighten the seton; if it falls out, inform the team (usually not an emergency unless pain, swelling, or fever develop).
• Skin and continence care: barrier creams, absorbent pads, and dignity; screen for low mood — perianal Crohn’s disease has a heavy psychological burden.
• Escalate by SBAR for new perianal swelling, fever above 38.0 °C, or rapidly increasing pain in an immunosuppressed patient.

💊 CROSS-SPECIALTY PRESCRIBING TRAP

• Steroids for perianal sepsis mask infection and do not heal fistulas.
• Loperamide or opioids in severe colitis can precipitate toxic megacolon.
• Repeated courses of antibiotics for recurrent “boils” near the anus delay the diagnosis of Crohn’s disease.

⛔ NEVER DO THIS

• Never perform or request a sphincterotomy, fistulotomy of a complex tract, haemorrhoidectomy, or tag excision in active Crohn’s disease.
• Never start or escalate biologics while an abscess is undrained.
• Never dismiss a third perianal abscess as “bad luck” — think Crohn’s.
• Never band haemorrhoids in active IBD (AGA 2026).

📝 COMMON DOCUMENTATION ERROR

• “Recurrent perianal abscess” with no record of bowel symptoms, weight, or blood tests.
• Fistula notes without the number and position of external openings, seton status, or IBD activity — making MRI and surgical planning harder.

📨 REFERRAL URGENCY BOX

The Patient in Front of You — Chapter 09 Mini-Case

🧑‍⚕️ THE PATIENT IN FRONT OF YOU

A 23-year-old woman attends with her third perianal abscess in 12 months; the previous two were drained in the ER. There are now two external openings at the left lateral and right posterior perianal skin, with large oedematous tags. She reports loose stools four times daily for 6 months and 5 kg of weight loss. Haemoglobin 108 g/L, CRP 38 mg/L, platelets 480 × 10⁹/L.

Step 1 Suspect Crohn’s disease: recurrent abscesses, multiple openings, oedematous tags, diarrhoea, weight loss, anaemia, and raised inflammatory markers.

Step 2 Control sepsis today: same-day drainage with a loose draining seton — no fistulotomy; biopsy and cultures.

Step 3 Investigate: faecal calprotectin, stool tests including C. difficile, HIV and STI testing, pelvic MRI, and ileocolonoscopy.

Step 4 Plan jointly: urgent gastroenterology review, pre-biologic screening, and infliximab once sepsis is controlled; smoking-cessation support if she smokes.

Board-Style Question — Chapter 09

A 31-year-old man with known ileocolonic Crohn’s disease and active proctitis has a complex trans-sphincteric fistula with an associated 3 cm abscess on MRI. What is the best initial management?

• A. Primary fistulotomy of the whole tract
• B. Drain the abscess and place a loose seton, then start anti-TNF therapy once sepsis is controlled
• C. Oral prednisolone 40 mg daily for 4 weeks
• D. Ciprofloxacin alone for 3 months

Answer and explanation

• ❌ A Fistulotomy of a complex tract in active proctitis risks non-healing wounds and incontinence.
• ✅ B Correct. Sepsis control (drainage and loose seton) comes first; infliximab is the recommended first-line biologic for perianal fistulising Crohn’s disease (AGA 2021), started once the abscess is drained.
• ❌ C Steroids do not heal fistulas and worsen undrained sepsis.
• ❌ D Antibiotics are adjuncts, not monotherapy for fistula remission (AGA 2021).

Ten-Item Rapid Revision Checklist — Chapter 09

• 01 I know perianal disease may precede intestinal Crohn’s disease.
• 02 I can list the features that distinguish Crohn’s-associated from idiopathic perianal disease.
• 03 I use the “suspect Crohn’s” checklist for recurrent abscesses and atypical fissures.
• 04 I request calprotectin, bloods, stool tests, and STI/HIV tests, and know a normal calprotectin does not exclude perianal Crohn’s.
• 05 I refer urgently to gastroenterology and colorectal surgery.
• 06 I never divide the sphincter in active Crohn’s disease.
• 07 I drain sepsis before biologics are started or escalated.
• 08 I know infliximab is the first-line biologic for perianal fistulas.
• 09 I know antibiotics are adjuncts, not monotherapy.
• 10 I teach seton care and screen for psychological distress.

Five Most Dangerous Mistakes — Chapter 09

1. ⚠️ Performing a sphincterotomy for a lateral fissure that was Crohn’s disease.
2. ⚠️ Laying open a complex Crohn’s fistula and causing incontinence.
3. ⚠️ Starting steroids or biologics with an undrained abscess.
4. ⚠️ Draining recurrent abscesses repeatedly without ever asking about bowel symptoms.
5. ⚠️ Missing carcinoma in a long-standing Crohn’s fistula that changed character.

Suggested Figure and Table Captions for the Medical Illustrator — Chapter 09

• Figure 9.1. Perianal Crohn’s disease: oedematous tags, lateral fissures, and multiple fistula openings.
• Figure 9.2. MRI fistula map with a loose draining seton in place.
• Figure 9.3. The combined medical–surgical pathway: drain, seton, biologic, repair.
• Table 9.1. Perianal manifestations of Crohn’s disease.
• Table 9.2. Idiopathic versus Crohn’s-associated perianal disease.
• Table 9.3. Work-up for suspected perianal Crohn’s disease.
• Table 9.4. Treatment principles.
• Table 9.5. Mimics of perianal Crohn’s disease.
• Algorithm 9.1. Perianal disease with possible Crohn’s disease.