**2. Pathophysiology and etiology**

The differential diagnosis of pruritus ani comprises a long list of conditions that can be grouped into infectious, inflammatory, and neoplastic. Primary or idiopathic pruritus ani accounts for more than half of cases (50–90%), and a variety of factors have been implicated in the pathophysiology (anatomic, dietary, hygienic, psychogenic, local irritants, and medications) [6]. However, fecal contamination and local skin irritation are the most common provoking factors. This phenomenon occurs by the activation of non-myelinated C-fibers in the epidermis and sub-dermis; though, the neurophysiological mechanisms behind the symptoms are much more complex. Scratching, although temporarily alleviates the itching sensation, is thought to produce inadequate feedback to inhibit further symptoms (*puritoceptive itching*). Therefore, avoiding scratching is key in the interruption of the vicious cycle of skin trauma, which is an additional stimulus for itching. In our practice, as part of routine interrogation and physical examination, we always inquire about products patients may have applied for symptomatic relief. Despite most patients denying fecal incontinence, many have some degree of leakage demonstrated during the examination of the perianal area and confirming the presence of stool.

*Infectious* Bacterial Fungal Viral Parasitic *Dermatologic* Psoriasis Lichen planus, lichen simplex chronicus, lichen sclerosus Contact dermatitis Atopic dermatitis Perianal psoriasis *Systemic diseases* Diabetes mellitus Leukemia, lymphoma, polycythemia vera Liver disease (hyperbillirubinemia) Chronic renal failure Thyroid disorders (hyperthyroidism) *Anorectal diseases* Benign Hemorrhoids (internal and external) Rectal prolapse (mucosal and full thickness) Fissure Fistula-in-ano Diarrhea Secreting villous tumors Fecal soiling and incontinence Skin tags Perianal Crohn's disease Hidradenitis suppurativa Malignant Anal canal and anal margin cancer Rectal cancer Bowen's disease Perianal Paget's disease *Miscellaneous* Radiation-induced dermatitis Vaginal discharge Urinary incontinence

**Table 1.** *Secondary pruritus—causes.*

*Perspective Chapter: Management of Pruritus Ani DOI: http://dx.doi.org/10.5772/intechopen.102782*

Several foods have been associated with the production of perianal itching and are commonly excluded from the diet as part of the initial management. These *pruritogenic foods* include coffee, colas, citrus fruits, chocolate, tea, energy drinks, alcoholic beverages, tomato, and spicy foods. They act as irritants of the perianal skin and have also been implicated in altering bowel habits, stool consistency, and facilitating seepage. A comprehensive history and physical examination are critical in narrowing the diagnosis since in many cases both primary and secondary etiologies can be found.

Secondary pruritus should be considered in cases where an identifiable cause is found. The etiologies in this group are very broad and can be classified into five categories—infectious, dermatologic, systemic disease, benign and malignant anorectal diseases, and miscellaneous (**Table 1**) [2, 3].
