What is the most likely diagnosis and recommended treatment for a 25‑year‑old with lifelong worsening pruritus ani, severe after defecation, despite excellent hygiene and prior albendazole therapy?

Lifelong Pruritus Ani: Most Likely Diagnosis and Treatment

The most likely diagnosis is pinworm infection (Enterobius vermicularis), and the patient requires proper diagnostic confirmation with the "sellotape test" followed by extended-course albendazole treatment, not just a single dose.

Why Pinworm is the Most Likely Diagnosis

Pinworm infection is the most common cause of pruritus ani in young adults, particularly when symptoms have persisted since childhood and worsen after defecation. 1 The key clinical features that point to pinworm in this case include:

• Lifelong history starting in childhood – pinworm is particularly prevalent in the pediatric age group and can persist into adulthood if inadequately treated 2, 3
• Severe itch after passing stools – this timing is characteristic because adult worms migrate to the perianal area, especially during and after defecation 1
• Recurrence after brief albendazole use – a single dose or short course is insufficient; pinworms require extended treatment 1
• Excellent hygiene doesn't prevent it – pinworm transmission occurs through auto-infection and fomite contamination, making it resistant to hygiene measures alone 1

Critical Diagnostic Error: Wrong Albendazole Regimen

The relative gave a single dose or short course of albendazole, which is the regimen for hookworm (400 mg single dose), NOT pinworm. 1 This explains why symptoms returned within 1-2 days.

For pinworm (Enterobius vermicularis), the correct regimen is albendazole 400 mg twice daily for 21 days with monitoring of liver function and full blood count. 1

Proper Diagnostic Confirmation Required

Before starting treatment, perform the "sellotape test" (also called the "cellulose tape test"): 1

• Place the sticky side of clear tape on the perianal skin first thing in the morning before bathing or defecation
• Remove the tape and place it on a glass slide
• Examine under microscope for pinworm eggs
• Repeat on 3 consecutive mornings if the first test is negative (eggs are eliminated intermittently) 1

Stool microscopy is NOT reliable for pinworm diagnosis because eggs are deposited on perianal skin, not in stool. 1

Complete Treatment Protocol

For the Patient:

Albendazole 400 mg orally twice daily for 21 days 1

• Monitor liver function tests and complete blood count during treatment 1
• This extended regimen is necessary because pinworm has a 2-6 week prepatent period, and shorter courses fail to eradicate all stages 1

For Household Members:

All close family members living in the same household must be treated simultaneously, even if asymptomatic. 3 Use the same albendazole regimen to prevent reinfection through the fecal-oral route and fomite transmission 1.

Environmental Measures:

• Wash all bedding, underwear, and towels in hot water on the first day of treatment 3
• Vacuum carpets and upholstered furniture 3
• Clean bathroom surfaces thoroughly 3
• Fumigation of living areas is NOT necessary 1

Alternative Diagnosis: Threadworm vs. Pinworm Confusion

Note that "threadworm" is simply another name for Enterobius vermicularis (pinworm) used in UK terminology. 1 Do not confuse this with Strongyloides stercoralis, which is a different parasite requiring different treatment 1.

Why Other Diagnoses Are Less Likely

Hemorrhoids:

• Hemorrhoids do NOT cause pruritus ani unless thrombosed 4
• Anal pain is generally not associated with uncomplicated hemorrhoids 4
• The lifelong history starting in childhood makes hemorrhoids extremely unlikely 4

Anal Fissure:

• Anal fissure causes severe pain during and after defecation, not primarily itching 5
• Fissures typically present with bright red bleeding and post-defecatory pain lasting hours 5
• The absence of pain in this case excludes fissure 5

Other Parasites:

• Hookworm causes "ground itch" at the site of larval skin penetration (feet), not perianal itch 1
• Whipworm (Trichuris) rarely causes pruritus ani 1
• Strongyloides would present with additional gastrointestinal symptoms and requires different treatment 1

Critical Pitfalls to Avoid

1. Never use a single dose of albendazole for pinworm – this is the hookworm regimen and will fail 1

2. Never treat the patient alone – all household members must be treated simultaneously to prevent reinfection 3

3. Never skip diagnostic confirmation – perform the sellotape test before assuming the diagnosis, even when clinical suspicion is high 1

4. Never attribute lifelong pruritus ani to "poor hygiene" – pinworm persists despite excellent hygiene due to auto-infection and environmental contamination 1

5. Never use mebendazole 100 mg as a single dose – while this is listed as an alternative for pinworm in some older guidelines 1, the most recent UK guidelines recommend the extended 21-day albendazole regimen for reliable eradication 1

When to Suspect Alternative Diagnoses

If the sellotape test is negative on 3 consecutive mornings AND symptoms persist after proper 21-day albendazole treatment with household member treatment, consider: 6, 7

• Perianal dermatitis from excessive cleaning or irritants 6
• Fecal soiling or incomplete wiping 7
• Dietary irritants (caffeine, citrus, spicy foods) 6
• Skin conditions (eczema, psoriasis, lichen sclerosus) 8

In these cases, refer to dermatology for further evaluation. 8