**2.1 Infectious**

Among the infectious agents, sexually transmitted diseases are common causes of anal pruritus, particularly in patients practicing anoreceptive intercourse. The most common pathogens are *Neisseria gonorrhoeae*, *Chlamydia trachomatis*, and *Treponema pallidum*, but herpes infections, molluscum contagiosum, and condyloma acuminatum (human papillomavirus infection) are also encountered (**Figure 1**). Herpetic lesions are typically painful vesicles with associated perianal burning sensation, that after rupture can leave superficial skin ulcerations (**Figure 2**). We often receive referrals of patients with a history of anoreceptive intercourse, as well as a large population of Human Immunodeficiency Virus (HIV) positive patients with perianal irritation. In most of these cases, symptoms are caused by undiagnosed sexually transmitted diseases (STD). Symptoms usually resolve after appropriate treatment.

In children, it has been well reported that *Beta-hemolytic streptococci* are involved in many cases of perianal dermatitis, whereas *Staphylococcus aureus* is frequently implicated in refractory dermatitis in adults. *Corynebacterium minutissimum* is the causative agent of erythrasma, a superficial infection of the intertriginous skin often seen in warm weather [7]. Fungal infections account for 10–43% of secondary anal pruritus, with *Candida albicans* being the most common fungi identified [8]. Parasitic perianal infections are rare, but common parasites identified include *Enterobius vermicularis* (pinworms), *Sarcoptes scabiei* (scabies), and pediculosis pubis [2]. Nocturnal and post-defecation pruritus ani in children is a characteristic symptom of pinworms infection. We do not have experience with pruritus ani in children since our practice is limited to adults only.

#### **2.2 Dermatologic**

A wide variety of dermatologic conditions have been associated with pruritus ani; hence, a detailed history and physical examination are essential. Perianal eczema is the most common condition responsible for anal pruritus. It originates as contact dermatitis to certain hygiene products or medications used to treat other anorectal conditions, such as over-the-counter hemorrhoid ointments, deodorants, scented wipes or toilet paper, and soaps. Inquiry about anal hygiene habits and products used must be part of the history. These patients often have a history of other atopic conditions, such as asthma. We typically encounter patients presenting with eczema after weeks of using over-the-counter products, such as moist wipes, and ointments to treat hemorrhoids.

**Figure 1.** *Perianal condyloma acuminatum.*

**Figure 2.** *Perianal herpes virus infection.*

Atopic dermatitis is another common cause of pruritus ani, with an estimated frequency of 15–20% of the population [8]. Psoriasis is another skin problem associated with perianal pruritus, and although not as common, reports in the literature vary from 5 to 50% [8, 9]. Other less common dermatologic conditions that cause pruritus ani include seborrheic dermatitis, lichen planus, lichen sclerosus, and

lichen simplex chronicus. A high index of suspicion is necessary for an adequate diagnosis and treatment.
