Perianal abscess is a surgical emergency — antibiotics without drainage are ineffective and allow the abscess to track along tissue planes (fistula formation). 30–40% of perianal abscesses are complicated by fistula-in-ano even with timely drainage. The standard treatment is surgical incision and drainage under general anaesthesia with a cruciate incision. Prescribing antibiotics alone for a perianal abscess is a well-documented cause of litigation. Anal squamous cell carcinoma (SCC) is HPV-associated and is increasing in incidence — it predominantly affects MSM (men who have sex with men) and HIV-positive individuals. Anal SCC is treatable with chemoradiotherapy (Nigro protocol) — early detection is therefore critical. Any persistent anal ulcer, lump, or pain in an HIV-positive patient or MSM should prompt urgent proctoscopy.

Anal fissure causes a classic pain pattern that is virtually diagnostic: severe sharp tearing pain during defecation, followed by a sustained burning ache lasting up to 60 minutes after defecation (sphincter spasm). This post-defecatory pain is caused by internal anal sphincter (IAS) spasm triggered by the fissure, which also reduces blood flow to the anoderm and perpetuates the fissure. The fear of painful defecation leads to stool withholding → constipation → harder stool → more pain — a self-perpetuating cycle. Breaking this cycle with topical GTN (relaxes IAS, increases local blood flow) plus stool softeners is the cornerstone of management. LGV (lymphogranuloma venereum) is an emerging cause of severe proctitis in MSM — it presents with bloody mucoid anal discharge, tenesmus, and severe rectal pain. It requires a specific NAAT test for chlamydia serovars L1-L3 and treatment with doxycycline 100 mg BD × 21 days (NOT the standard 7-day course).

Fissures not in the posterior midline (atypical fissures) — at lateral positions, or multiple fissures — suggest secondary causes: Crohn's disease, anal cancer, syphilitic ulcer, HSV, tuberculosis. Atypical fissures mandate colonoscopy and STI screen before attributing to primary fissure disease. Thrombosed external haemorrhoids (TEH) are one of the most painful acute conditions seen in primary care — surgical excision within 72 hours of onset dramatically reduces pain and size. After 72 hours, conservative management (ice, analgesia, stool softeners, sitz baths) is preferred as surgical intervention becomes more hazardous due to oedema, and spontaneous resolution occurs over 2–3 weeks. Patients presenting at 2–3 weeks can be reassured that the worst is over.

Topical lidocaine 5% ointment applied inside and around the anal margin 5 minutes before PR examination dramatically reduces pain and allows examination in most patients with anal fissure. This is simple and available on prescription — GPs should use it routinely rather than deferring all examinations. HbA1c should be measured in all patients with perianal abscess — diabetes is present in 15–20% of patients with perianal suppurative disease and significantly worsens outcomes. Recurrent or unusually extensive perianal sepsis in a patient without a known diabetes diagnosis should prompt urgent HbA1c testing. Stool calprotectin is a useful non-invasive marker of intestinal inflammation — an elevated result in a patient with recurrent fissures at atypical positions should prompt colonoscopy to exclude Crohn's disease.

Chronic anal fissure (present >6 weeks, indurated edges, sentinel pile) that fails topical treatment has two surgical options: botulinum toxin injection (30–40% recurrence, low side effects) or lateral internal sphincterotomy (LIS — 95% healing rate, but 5–10% risk of minor incontinence). LIS is more effective but the incontinence risk must be discussed carefully. Botulinum toxin is preferred in women (especially post-obstetric injury, high baseline incontinence risk) and in patients with Crohn's disease. The GP's role is to ensure topical treatment is applied correctly and adequately (sufficient dose, adequate duration) before referring for surgery.

GTN 0.4% ointment for anal fissure works by releasing nitric oxide, which relaxes the internal anal sphincter — reducing sphincter pressure by 20–30% relieves the ischaemic component of fissure pain and allows healing. The headache side effect (from systemic GTN absorption through the perianal mucosa) can be minimised by using the smallest effective amount (pea-sized, fingertip) and applying distal to the anal margin rather than deep inside. Diltiazem 2% ointment is equally effective with fewer headaches (calcium channel blocker mechanism) and is preferred in patients who cannot tolerate GTN headaches. The critical teaching point: stool softening must accompany all topical treatments — topical treatment alone without addressing the underlying constipation/hard stool will fail.

Perianal abscesses almost always originate in the anal glands (cryptoglandular theory) — there are 4–10 anal glands that open into the crypts at the dentate line. Infection tracks along tissue planes (intersphincteric, perianal, ischiorectal, or supralevator spaces) depending on which direction it travels. The surgeon must probe the abscess cavity at the time of drainage to identify any fistula tract and lay it open if present — this is not possible under local anaesthesia in a GP surgery. Missing a fistula tract at the initial drainage leads to abscess recurrence in 30–40% of cases. The surgical approach also allows comprehensive examination under anaesthesia for associated conditions (Crohn's fistula, anal cancer in the cavity wall).

Anal squamous cell carcinoma incidence in HIV-positive MSM is 80-fold higher than the general population — it is now a major cancer concern in this group, and screening with anal cytology (Pap smear equivalent) is increasingly recommended. HPV vaccination (Gardasil 9) prevents infection with high-risk HPV types 16 and 18, which cause 90% of anal SCCs. The NHS HPV vaccination programme covers girls and MSM up to age 45 — opportunistic checking of vaccination status in MSM patients presenting with anorectal symptoms is an important prevention opportunity. The footstool/squatting position (knees above hips) during defecation significantly reduces anorectal muscle strain — it aligns the puborectalis muscle in a relaxed position rather than the constipated acute angle created by sitting on a standard toilet.

Post-operative fistula after perianal abscess drainage affects 30–40% of patients — the GP plays a crucial role in recognising it. Signs are persistent perianal discharge through a small external opening after the abscess wound appears healed, or recurrent abscess at the same site. Failure to refer to colorectal for fistula assessment leads to repeated abscess cycles and increasing sphincter damage. MRI fistula is the gold standard imaging for mapping complex fistula tracts, particularly in Crohn's disease where conservative surgical approaches are needed to preserve sphincter function. All patients with anorectal symptoms should be informed that they can present back at any time with new symptoms — chronic anorectal disease has a high rate of new problems developing.