Description

• Intense anal/perianal itching and/or burning
• Usually acute (defined as <6 weeks of symptoms)
• Classified as primary (idiopathic) or secondary (25–75% of cases) to anorectal pathology

Epidemiology

Incidence

• 1–5% of the general population
• Predominant age: 30 to 50 years; although seen in all age groups
• Predominant sex: male > female (4:1)

Prevalence
Difficult to estimate because many patients do not report symptoms; affects 1–5% of the population

Etiology and Pathophysiology

• Multiple etiologies categorized by inflammatory, infectious, systemic, neoplastic, anorectal disorders, neuropathic, neurogenic, and psychogenic causes (1),(2)
• Most cases are idiopathic (25–90%), which are likely due to trauma from wiping or scratching and perianal fecal contamination.
  • Soilage can be due to an abnormality of rectoanal inhibitory reflex and a lower threshold or transient internal anal sphincter relaxation.
• Depending on underlying etiology, itch pathway may be histamine mediated or nonhistamine mediated (1).
• Pruritus ani is typically intensely perceived by the patient due to dense innervation.
• Etiologies of secondary pruritus ani:
  • Inflammatory dermatologic diseases:
    • Allergic contact dermatitis (soaps, perfumes, or dyes in toilet paper, topical anesthetics, oral antibiotics)
    • Atopic dermatitis ± lichen simplex chronicus (Patients may also have asthma and/or eczema.)
    • Psoriasis (Lesions tend to be poorly demarcated, pale, and nonscaling.)
    • Seborrheic dermatitis
    • Scleroderma
    • Lichen planus (may be seen in patients with ulcerative colitis and myasthenia gravis)
    • Hidradenitis suppurativa
    • Radiation dermatitis (2)
  • Colorectal/anorectal diseases: rectal prolapse, hemorrhoids, fissures or fistulas, proctitis, chronic diarrhea/constipation, polyps
  • Infectious etiologies may be sexually transmitted: bacteria (gonorrhea, chlamydia, syphilis), viruses (herpes simplex virus [HSV], condyloma acuminata from human papillomavirus [HPV], molluscum), parasites (pinworms, lice, scabies, or bed bugs), fungi (Candida or dermatophytes like tinea); other bacteria (Staphylococcus aureus, β-hemolytic Streptococcus, Corynebacterium minutissimum [erythrasma]) (2)
  • Malignancies: melanoma, basal cell/squamous cell carcinoma, colorectal cancer, leukemia, lymphoma, or (uncommon) the presenting symptom of Bowen or Paget disease
  • Mechanical factors: vigorous cleaning and scrubbing, tight-fitting clothes, synthetic undergarments
  • Systemic diseases (often presents as generalized pruritus): diabetes mellitus (most common), cholestasis, chronic liver disease, renal failure, hyperthyroidism, anemia, HIV, vitamin or iron deficiencies, lumbosacral radiculopathy (particularly in the elderly)
  • Chemical irritants: local anesthetics, chemotherapy, diarrhea (often from antibiotic use)
  • Dietary elements (citrus, milk products, coffee, tea, cola, chocolate, beer, wine, tomatoes, nuts)
  • Psychogenic factors: anxiety–itch–anxiety cycle

Risk Factors

• Obesity
• Excess perianal hair growth and/or perspiration
• Underlying anorectal pathology
• Atopic disease
• Underlying anxiety disorder
• Caffeine intake has been correlated with symptoms.

General Prevention

• Good perianal hygiene; avoid overzealous cleaning.
• Avoid mechanical irritation of skin (vigorous cleaning or rubbing with dry toilet paper or baby wipes, harsh soaps or perfumed products, excessive scratching with fingernails, or tight/synthetic undergarments).
• Minimize moisture in perianal area (absorbent cotton in anal cleft may help keep area dry).
• Avoid laxative use (loose stool is an irritant).

Commonly Associated Conditions

• Psoriasis is seen in 5–55% of patients with pruritus ani.
• Coexisting anorectal disease, such as hemorrhoids, can be seen in up to 52% of patients with pruritus ani.