What are the differential diagnoses for anal pain and the recommended evaluation and management?

Differential Diagnosis for Anal Pain

Most Common Causes

Anal fissure is the most likely diagnosis when severe pain accompanies defecation, while perianal abscess should be suspected with fever and swelling, and thrombosed external hemorrhoids present with acute pain and a palpable tender mass. 1, 2

Acute Anal Fissure

• Cardinal feature: Severe pain during and after bowel movements that may persist for hours, accompanied by minor bright-red rectal bleeding on toilet paper 1, 2, 3
• Location: Typically posterior midline; off-midline fissures warrant evaluation for inflammatory bowel disease, HIV/AIDS, tuberculosis, syphilis, leukemia, or malignancy 2
• Visualization: Best seen by everting the anal canal with opposing thumb traction during inspection 2
• Chronic features: Sentinel skin tags, hypertrophied anal papillae, fibrosis, and visible internal sphincter muscle at the base 2

Perianal/Perirectal Abscess

• Presentation: Throbbing anal pain with fever, perianal swelling, and exquisite tenderness 1
• Classification: Perianal (most superficial), intersphincteric, ischiorectal, or supralevator 1, 4
• Key distinction: Significant systemic symptoms with high abscesses (supralevator, high ischiorectal) but few local findings; low abscesses show obvious swelling and cellulitis 1
• Digital exam: May reveal tender indurated area above the anorectal ring, though examination may be intolerably painful 2

Thrombosed External Hemorrhoids

• Presentation: Acute onset of severe anal pain with a palpable, tender, bluish perianal mass 2, 5, 6
• Critical distinction: Uncomplicated internal hemorrhoids do NOT cause pain—pain indicates thrombosis 2, 7
• Timing: Surgical excision is indicated only if within 48-72 hours of pain onset 4, 6

Hemorrhoidal Crisis (Prolapsed/Strangulated Hemorrhoids)

• Presentation: Acutely prolapsed, edematous, and painful hemorrhoidal tissue that cannot be reduced 1
• Important caveat: Up to 20% of patients with hemorrhoids have a concurrent anal fissure; when pain is present, fissure is the more likely primary pathology 2

Functional/Chronic Pain Syndromes

Proctalgia Fugax

• Presentation: Brief (seconds to minutes), severe, cramping rectal pain that occurs spontaneously, often at night, without associated bleeding or defecation 7, 8
• Diagnosis of exclusion: Requires thorough examination including digital rectal exam and anoscopy to exclude organic pathology 7

Levator Ani Syndrome

• Presentation: Chronic, dull, aching rectal or pelvic pain lasting ≥20 minutes, often worse with sitting 8
• Physical finding: Tenderness on posterior traction of the puborectalis muscle during digital rectal examination 8

Less Common but Critical Diagnoses

Fournier's Gangrene

• Red flags: Severe pain with systemic toxicity, crepitus, skin necrosis, or rapidly progressive cellulitis 1
• Urgency: Requires immediate surgical debridement and broad-spectrum antibiotics 1

Anal Carcinoma

• Presentation: Rectal bleeding (most common), anal mass, or persistent ulceration 4
• High-risk features: Atypical fissure location, non-healing ulcer, or indurated mass warrants biopsy 2, 4

Sexually Transmitted Infections (Proctitis)

• Presentation: Rectal pain, discharge, tenesmus, or perianal ulcers in patients with anoreceptive intercourse 4
• Pathogens: HSV-2, gonorrhea, chlamydia, syphilis 4

Diagnostic Approach Algorithm

Step 1: History—Timing and Character of Pain

• Pain during/after defecation with bleeding: Anal fissure 2, 3
• Constant throbbing pain with fever: Perianal abscess 1
• Acute pain with palpable lump: Thrombosed external hemorrhoid 2, 6
• Brief, severe, spontaneous cramping: Proctalgia fugax 7, 8

Step 2: Visual Inspection with Buttock Traction

• Posterior midline tear: Anal fissure 2
• Perianal swelling, erythema, fluctuance: Abscess 1
• Bluish, tender perianal mass: Thrombosed external hemorrhoid 2

Step 3: Digital Rectal Examination

• Defer if acute fissure suspected (intolerably painful) 2
• Perform to exclude abscess: Tender indurated area above anorectal ring 2
• Levator tenderness on posterior traction: Levator ani syndrome 8

Step 4: Anoscopy

• Mandatory if hemorrhoids suspected to avoid missing other pathology 2, 5
• Visualizes internal hemorrhoids, fissures, masses 6

Step 5: Imaging—Only for Suspected Complications

• CT scan or MRI: Only if suspicion of concomitant anorectal disease (sepsis/abscess, inflammatory bowel disease, neoplasm) 1
• Not indicated for typical fissure, thrombosed hemorrhoid, or proctalgia fugax 7

Critical Pitfalls to Avoid

• Never assume hemorrhoids without anoscopy—up to 20% have concurrent fissures, and pain mandates evaluation for fissure or other pathology 2, 5
• Do not prescribe antibiotics for uncomplicated fissure or proctalgia fugax—these are not infectious processes 1, 7
• Do not delay drainage of perianal abscess—prompt surgical incision and drainage prevents serious complications 1, 4
• Do not miss Fournier's gangrene—systemic toxicity with anal pain requires immediate surgical consultation 1
• Biopsy atypical or non-healing lesions—off-midline fissures, indurated masses, or persistent ulcers may represent malignancy or systemic disease 2, 4