The itchy bottom: causes and treatment

Anal pruritus is itching of the perianal region. It can also include soreness sensations and even severe burning pain [1‐5]. The first mention of pruritus ani was probably in an Egyptian papyrus [4].

Anal itching affects about 1 to 5% of the population, with a higher prevalence in men (4:1) [1‐9]. It is more frequent in the adult population between 40 and 60 years old [2, 4, 7, 8]. It represents the second most common proctological complaint after haemorrhoids [7].

Physiopathology of anal pruritus is not fully understood. It is supposed to be initiated by C‑fibres in the skin, with the implication of itching mediators such as bradykinin, histamine and kallikrein. Thus, the information of pruritus would be transmitted to the brain with inadequate feedback, under the threshold of pain. It is believed that it implies a vicious circle of itching and scratching, increasing irritation and inflammation, and thus symptoms (Fig. 1). Moreover, faecal soiling of the perianal region is probably included in the irritation, sometimes associated with anal sphincter dysfunction or anatomical changes associated with proctological diseases [1, 2, 4, 5, 8]. Caplan, in 1966, applied a patch test with autologous faeces on the perianal region and on the arm. They showed that faecal soiling did not have the same effect in the perianal region as on other cutaneous surfaces [4, 10].

About 100 possible causes have been identified. It can be classified into primary (idiopathic) or secondary. Idiopathic pruritus ani remains an exclusion diagnosis [3]. Main secondary causes can be classified into local irritation, infections, proctological diseases, neoplastic lesions, dermatological and systemic diseases, and other aetiologies. Psychological factors can also be implied [1‐4, 7‐9]. Secondary causes are given in more detail in Table 1 and are discussed through history and examination. Literature is conflicting about the proportion of secondary causes, since some studies assume that they account for 25 to 75% of the cases [2, 8], and others cite 10 to 50% [3]. Distribution of the secondary causes is also different in children [5], and is not discussed here.

Few clinical classifications have been proposed regarding the severity of the manifestations. Kuehn et al. identified four stages of disease: mild, moderate, severe and chronic [11]. The Washington Hospital Center also defined a four-subtype classification depending on the severity of skin lesions, from stage 0 to 3 [1, 2, 4]. However, in daily clinical practice, such classifications do not seem very useful.

For the purpose of this review, we divided the various aetiologies into seven groups (Fig. 1).

An algorithm for the diagnostic tools and treatments of anal pruritus is proposed in Table 1.

Rigorous history taking is mandatory to identify a potential secondary cause, and thus to be able to propose an adapted treatment.

First, the timing of onset and factors associated with worsening of the symptoms must be identified. Thus, one must seek variations with ambient temperature, an increase at night or with physical exercise [1, 2, 4, 7, 12]. Factors associated with local irritation must be questioned: moisture, clothing (synthetic tissues) or use of chemical products such as laundry detergents or perfumed topical products. Moreover, food or beverages can be implied, such as coffee, tea, milk, cola, spicy food, alcohol, as well as tobacco. Frequently implied foods are citrus fruits, chocolate, nuts and tomatoes [1‐4, 6‐8, 12].

Second, proctological symptoms should be identified, and faecal habits defined. Identification of frequency, consistency of stools and history of incontinence is a mandatary point. Perianal faecal soiling is one of the main causes of anal itching. Past proctological interventions should be discussed. Hygiene habits must be questioned, such as the use of soaps and wipes. Excessive scrubbing of the perianal region can lead to mechanical lesions inducing pruritus [1‐4, 6‐8, 12]. Patients may report spotting of blood on the toilet paper from cutaneous excoriations [2].

Finally, comorbidities and familial history should be addressed, to identify a potential systemic or neoplastic related disease. As such, allergies, infectious diseases affecting other members of the family and dermatological diseases can cause anal pruritus. Moreover, the use of systemic or local medications should be signalled, such as steroids, laxatives and colchicine [1, 6]. Recent travel and sexual habits must also be queried [12].

A systemic evaluation should search for other dermatological lesions that could be associated with systemic diseases potentially responsible for anal pruritus, such as psoriasis, atopic dermatitis, lichen sclerosis and planus [1, 7, 8, 13]. Atopic dermatitis presents with thickened skin, dry erythematous or excoriated lesions of the perianal region and other localisations, and familial history is commonly positive [1, 2]. Psoriasis induces erythematous plaques with sharp edges [8]. Lesions are typically dry, with white scales, and in a butterfly shape [2]. Lichen sclerosis is associated with white atrophic skin, usually extends to the anterior perineum and is more frequent in women [2, 8].

Infections can be found on physical examination, including sexually transmitted diseases [2]. Bacterial infections include β‑haemolytic streptococci, Corynebacterium minutissimum (erythrasma) and Staphylococcus aureus. Candida species are frequently involved (10% of the cases [2]). Clinical manifestations of Candida infection include association with lesions in the groin or other folds. Erythema is typically bright [8] with satellite lesions and it often affects obese, elderly or immunosuppressed patients (Fig. 2; [2]). Other pathogens include Tinea cruris, pinworms (Enterobius vermicularis), pediculosis and scabies. Sexually transmitted diseases include Herpes Simplex Virus (HSV), Human Papillomavirus (HPV), gonorrhoea, Chlamydia, syphilis and Human Immunodeficiency Virus (HIV) [1, 7, 8].

Second, a proctological examination should be performed. This includes perineal and genital examination. The skin can present with different lesions, from erythema to excoriations and lichenification [1, 6]. Contact dermatitis typically presents with macular erythema, hyperkeratosis and radial fissures (Fig. 3; [1]). Anorectal digital examination and anoscopy are also important, searching for an associated proctological disease such as haemorrhoids, anal fistula or fissure and rectal prolapse [1, 3, 7, 8, 12]. Haemorrhoidal prolapse is the most frequent cause of anal pruritus associated with a proctological disease (Fig. 4; [8]). Examination at rest and using the Valsalva manoeuvre can help the diagnosis. Some proctological conditions can be associated with increased soiling and poorer hygiene, such as skin tags [2, 6]. Sometimes, assessment under general anaesthesia is even necessary to exclude a concomitant proctological disease [7].

Depending on symptoms at medical history and clinical examination, further investigations are needed. Treatment should be directed through whatever causing factor that has been identified. Proposed additional examinations and treatments are summarised in Table 1.

Anal pruritus is a common source of proctological consultations, and the appropriate management depends on the identification of a potential secondary cause through rigorous history taking, physical examination and directed complementary investigations. The treatment relies on the identification of a potential aetiology, and should be based on a step-up approach. Little evidence supports the use of specific medications to alleviate symptoms.