What are the differential diagnoses and treatment recommendations for perianal pruritus, including in children?

Perianal Itching: Differential Diagnosis and Treatment

Primary Differential Diagnoses

The most common causes of perianal pruritus differ significantly between children and adults, requiring age-specific diagnostic approaches.

In Children

• Pinworm (Enterobius vermicularis) is the most frequent cause of perianal itching in children, presenting with intense nocturnal pruritus 1
• Diagnosis is confirmed by the "sellotape test": apply sticky side of tape to perianal skin in the morning and examine microscopically for ova 1
• Perianal streptococcal dermatitis (Streptococcus pyogenes) presents with perianal erythema, itching, and sometimes fissures in children aged 1-8 years 2
• Lichen sclerosus affects 7-15% of pediatric cases, presenting with porcelain-white lesions, ecchymosis (potentially mistaken for sexual abuse), and perianal involvement in 30% of cases 1
• Perianal Crohn's disease occurs in 15-25% of pediatric Crohn's patients, manifesting as fistulas or abscesses 1

In Adults

• Primary (idiopathic) pruritus ani from fecal soiling or food irritants is the most common cause 3, 4
• Lichen sclerosus presents with porcelain-white plaques, ecchymosis, and figure-eight distribution around vulva and anus in women (30% have perianal involvement); perianal disease is extremely rare in males 1
• Hemorrhoids, anal fissures, and fistulas cause secondary pruritus through moisture and irritation 5
• Candida or dermatophyte infections identified in perianal cultures, though often secondary to underlying anorectal pathology 5
• Contact dermatitis (irritant, allergic, or atopic) from excessive cleaning, toilet paper, or topical agents 6

Treatment Algorithm

Step 1: Age-Specific Initial Management

For Children:

• If pinworm suspected: Treat empirically with albendazole 400 mg single dose OR mebendazole 100 mg single dose 1
• If perianal streptococcal dermatitis: Oral penicillin plus topical mupirocin or fusidic acid 2
• If lichen sclerosus confirmed: High-potency topical corticosteroids (though specific pediatric regimens require specialist guidance) 1
• If Crohn's-related perianal disease: MRI pelvis with IV contrast for anatomic assessment, followed by ciprofloxacin 20 mg/kg/day for 10 weeks as bridge to immunosuppressive therapy 1, 7

For Adults:

• Eliminate irritants first: Stop excessive washing, harsh soaps, and topical agents 3
• Apply emollients (sorbolene) to protect skin 3
• Short course topical hydrocortisone cream (apply to affected area 3-4 times daily for adults; not more than 3-4 times daily for external anal itching) 8, 3

Step 2: Address Underlying Anorectal Pathology

• Treat hemorrhoids, fissures, or anal spasm surgically or medically as indicated 5
• In one study, 20 of 23 patients with pruritus and perianal mycosis had resolution after treating underlying proctological disease without antifungal therapy 5
• Reserve antifungal therapy (econazole or similar) only if fungal infection persists after treating underlying anorectal pathology 5

Step 3: Refractory Cases

• Capsaicin cream for chronic cases unresponsive to initial measures 3
• Reassess diagnosis if symptoms persist despite appropriate therapy 4
• Consider biopsy if lichen sclerosus, malignancy, or inflammatory conditions suspected 1, 4

Critical Diagnostic Pitfalls

• Do not mistake lichen sclerosus ecchymosis for sexual abuse in children, though recognize that LS can coexist with or be triggered by abuse (Koebner phenomenon) 1
• Do not use antibiotics alone for perianal abscess—incision and drainage is definitive treatment 9, 7
• Do not perform routine fistulotomy in infants under 1 year with perianal abscess, as the condition is often self-limited 10
• Do not overlook Crohn's disease in children with perianal fistulas; MRI pelvis with IV contrast has 81-100% sensitivity/specificity 1
• Avoid treating perianal mycosis with antifungals before addressing underlying anorectal pathology, as fungal colonization is often secondary 5

Special Populations

Immunocompromised Patients with Perianal Abscess

• Require antibiotics plus surgical drainage: metronidazole 500 mg IV/PO every 8 hours PLUS ciprofloxacin 400 mg IV every 12 hours or 750 mg PO every 12 hours 9, 7
• Duration: 7-14 days for non-Crohn's abscess; 10 weeks for Crohn's-related disease 9, 7

Pregnant Women with Trichomoniasis

• Symptomatic pregnant women should be treated with metronidazole 2 g single dose to ameliorate symptoms, though this does not address perianal pruritus specifically 1