Pruritus ani (PA) is a common skin disorder that manifests as itching arising in the anal or perianal areas, which usually produces serious discomfort in the patient, and is frequently misdiagnosed as “hemorrhoids” (1). Although it is the skin immediately adjacent to the anal margin that is most frequently affected, symptoms may arise in the natal cleft or anteriorly up to and including the scrotum or vulva (2).
The true prevalence of PA is difficult to evaluate because the majority of individuals do not consult a physician (3). It has been suggested, however, that it affects from 1% to 5% of a general population, most frequently men, with a male to female rate of 3.7:1 (4).
Pruritus ani has been considered by some authors as “probably the least researched everyday symptom from which humans suffer” (5).
Perianal itch is a physical condition. The nerves responsible for pruritus are unmyelinated C fibers. Histamine is the main peripheral mediator of pruritus, but compounds like serotonin, prostigmine, neuropeptides, and endogenous opioides have also been incriminated in the physiopathological mechanism of the itch (6). The events leading to PA are presented in Figure 1 (7).
Most cases of PA are secondary to a precipitating factor such as infectious agents, excessive use of soap and detergents, fecal soilage, and dietary irritants, which account for the majority of cases of anal pruritus (Table 1). The most common causes of the condition vary according to the age group of the patients and their socioeconomic condition. In children, the most frequent causes of PA are probably infectious in origin. Among the intestinal infestations, pinworm is the most common cause of PA in children (8). Pinworm is a highly contagious intestinal parasitic infestation considered to be common in children. In the United States, pinworms are found with a high prevalence in day care settings and in urban areas. It is considered that approximately 20% of children in the United States will develop pinworm at some point in their lives because the parasite is easily spread through a fecal-oral route (1,8). In these cases, PA occurs predominantly at night and is caused by an inflammatory reaction due to the presence of adult worms and eggs on the perianal skin. When the host scratches, eggs become lodged under the fingernails, thereby augmenting transmission (8). Secondary bacterial infections may occur if the excoriation is severe (1,8). In a series of 154 schoolchildren ages 6 to 12 years in a rural population in Venezuela, pinworm showed a prevalence of 58% and anal pruritus was the most common clinical finding (>50% of the infested cases) (9). Hymenopelis nana infection is another parasite that can cause PA and has been shown to be highly prevalent in the stool examinations of 2083 Thai children (10). Other less frequent causes for PA in children include scabies, candida, and herpes (6). Dietary agents such as coffee, cola, chocolate, milk, and beer have also been implicated as causative agents for PA, especially in adults.
Anal pruritus can also result from a number of skin diseases, including contact dermatitis, psoriasis, atopic dermatitis, hidradenitis suppurativa, and Paget disease. In the United Kingdom, perianal dermatoses are frequently diagnosed in children with PA (6). Diaper dermatitis is a common cause of PA in infants before sphincter control (6,11).
In a prospective study of 126 patients with perianal dermatitis ages 7 to 82 years over a period of 4 years, the authors found that most of the patients (51.6%) had complaints persisting for more than 12 months. The clinical diagnosis in 68 patients (54%) was as follows: intertrigo/candidiasis (42.9%), atopic dermatitis (6.3%), PA (5.6%), psoriasis (3.2%), skin atrophy from steroid use (2.4%), lichen sclerosus et atrophicus (n = 2), herpes simplex (n = 1), and condylomata acuminata (n = 1) (12).
Several clinical trials have demonstrated that PA may be a symptom of a benign or malignant colon and/or anorectal pathology. Daniel et al (4) evaluated the causes of anal pruritus in a prospective study that included 109 adult patients who had anal pruritus as the only presenting symptom. All patients underwent anoscopy, rigid proctoscopy, and colonoscopy. The mean age of the cohort was 52, with a ratio of men to women of 2 to 1. Symptoms were present for an average of 6 weeks before presentation. The authors demonstrated that 25% of the patients had idiopathic pruritus, whereas 75% had coexisting pathology in the colon or anorectum including hemorrhoids (20%), anal fissures (12%), rectal cancer (11%), anal cancer (6%), adenomatous polyps (4%), and colon cancer (2%). The contribution of polyps and colon cancer to the pruritus was uncertain. Patients who had pruritus associated with cancer had a significantly longer duration of symptoms than patients with benign causes.
Fecal soiling in patients with PA can result from any cause of diarrhea, loose stools, or encopresis; in addition, some patients have a primary abnormality of the rectoanal inhibitory reflex and a lower threshold for internal anal sphincter relaxation (13).
It should be noted that sometimes PA is not associated with any primary condition. In these circumstances the condition is defined as idiopathic and has been considered to be linked to functional causes or to a disturbance of psychological or psychiatric origins (6).
CLINICAL PRESENTATION AND DIAGNOSIS
Although itching causes scratching, this does not occur before the age of 3 months (14). Other symptoms include irritability, sleep disturbance, and decreased appetite (1). A complete anal and rectal examination should be performed to look for specific causes, especially pinworm. The physical examination may reveal perianal dermatitis and excoriation around the anus from persistent scratching. Patients may have an easily recognizable condition such as anal fissures, anal fistulas, papillomas, skin tags, external hemorrhoids, or rectal prolapse. Any condition that hampers efficient wiping of the anus may allow small particles of feces to accumulate on the perianal skin and act as an irritant. Excessive sweating exacerbated by poorly fitting undergarments along with poor personal hygiene may also be noted (7). A thorough history of dietary and hygiene habits is also helpful. Sometimes vaginal irritation can also be noted. Pinworm can be easily diagnosed by applying a transparent adhesive tape to the skin around the anus before bathing or using the toilet in the morning. The tape is transferred to a slide and the presence of pinworm eggs may be confirmed by microscopy (1). Other parasites can be diagnosed by the examination of stool samples. As previously stated, PA can result from specific skin diseases, among others, psoriasis, contact dermatitis, atopic dermatitis, hydradenitis suppurativa and Paget disease. In these cases, PA will usually be 1 manifestation of a more generalized condition.
Because most causes of anal pruritus are secondary, treatment should be directed at the underlying etiology (1). Once these have been excluded, both general and specific measures must be initiated. General measures include limiting constipation and diarrhea appropriately with either a high-fiber diet or stool softeners (15). PA may not be easily amenable to treatment because it can be the result of a self-perpetuating cycle (1).
For pinworm infestation, initial treatment consists of patient and family education about hygiene and fecal-oral spread. General measures, such as hand washing, keeping fingernails short and clean, laundering all bed linens twice weekly, and cleaning toilet seats daily, can usually eliminate the problem in 1 to 2 weeks (1). Either mebendazole or albendazole should be used as first-line treatment of pinworm infection. A single 100-mg dose of mebendazole results in a mean cure rate of 95%, but a second dose is often given after 1 to 2 weeks to help prevent recurrences due to reinfection (16). Albendazole is given at a dose of 100 mg if the patient is <2 years old or 400 mg if older. A single dose of albendazole repeated for 2 weeks achieves a cure rate close to 100% (17). Both drugs are extremely well tolerated. It should be remembered that reinfection is highly common with pinworms and a repeated treatment course should be considered (7).
In those cases of PA not attributable to pinworm or other primary causes, reassurance, patient education, and follow-up are key elements of treatment. Stopping scratching, although difficult to achieve, can often break the itching cycle (1).
The management of idiopathic PA, especially in children, is based more on anecdote than on scientific evidence (18). There are few evidence-based guidelines in the medical literature on the treatment of this relatively common condition. Perineal hygiene is thought to be important and is said to improve symptoms (7,15,18,19). During initial management, toilet paper use after a bowel movement may be abrasive. Patients may find more comfort in wiping with synthetic cotton swabs premoistened with warm water. Vigorous rubbing should be avoided (15). Topical preparations such as those containing tannic acid or zinc-containing pastes have been used, but evidence of their efficacy or complications is lacking (18). Preparations of topical steroids have been used in uncontrolled trials and have been reported to be beneficial (6,20). However, there is concern that steroids may sensitize the skin and that their long-term use may cause troublesome skin atrophy (18). Topical capsaicin (0.006%) has been shown to be an effective treatment in a randomized study in adults with idiopathic PA (21). It has been proposed that in these patients there is a phenotypic change in polymodal sensory fibers that normally express the capsaicin/heat receptor (VR1 [vanniloid receptor-1]) (22). Our experience with this modality in children with idiopathic PA failed, and it caused further irritation.
In their randomized controlled crossover pilot study, Al-Ghnaniem et al (18) have demonstrated the efficacy (measured by visual analogue scale and by dermatologic quality of life questionnaire) of local 1% hydrocortisone in white soft paraffin over placebo (white soft paraffin) in adults with PA. Another approach in adults is the injection of methylene blue used in solution with hydrocortisone and lignocaine. It has been shown to achieve effective control of PA in 88% of patients who have failed to respond to standard dermatological, hygiene, and surgical treatments (23). There is evidence from electron microscopy studies that methylene blue acts by destroying sensory nerve endings in the treated skin (24). The effect of sensory nerve ending destruction is to desensitize the perianal skin, thus breaking the desire to scratch, and with it the itch–scratch cycle.
The value of an injection of a sclerosant consisting of 5% solution of phenol in almond oil injected into the perianal subcutaneous tissues in order to destroy the epithelial debris in this area, which is believed to be the primary cause of idiopathic PA, has been described by Shafik for 96 adult patients with idiopathic PA who failed conservative therapy (25). Cure was obtained in 85 patients (88.5%).
In summary, PA is frequently encountered in children by the primary care physician and the pediatrician. It is mainly due to an infection with pinworms, but fecal soiling, poor hygiene, local irritation, and dietary agents should also be considered. Treatment should be directed at the underlying etiology. Once these have been excluded, both general and specific measures must be initiated. There is almost no experience for local treatment modalities in children, and they cannot currently be recommended.
We thank Prof Michael Jaffe for helpful comments.
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