Itching of the anus is a common condition afflicting up to 5% of the population.2
The incidence of primary and secondary pruritus ani varies among different studies. Several studies show that the incidence of idiopathic pruritus ani is 75–95%.9
Other authors have found that its incidence is only 25%.10
Characteristically, pruritus ani is exacerbated by friction or a warm moist perineal environment. Poor anal hygiene or, in contrast, overcleansing with soap is often a contributing factor. Patients with idiopathic pruritus ani have been found to have abnormal transient internal sphincter relaxation11
and an abnormally profound decrease in anal canal pressure during rectal distention, as well as early incontinence on saline continence tests, implying that intermittent seepage from the anal canal may be a causative factor.12
A decrease in resting anal canal pressure with coffee intake has also been reported13
which may explain the documented exacerbation of symptoms with ingestion of caffeine. Treatment of idiopathic pruritus ani is non-specific and is aimed at restoring clean dry intact skin. The perineum must be gently cleaned with water after defecation. Drying should also be done gently, preferably with a hair dryer. The perineum may be cleaned several times a day with water premoistened wipes to absorb seepage material. Patients should be advised on the use of emulsifying ointment as a soap substitute, and not to shampoo their hair in the bath. Avoidance of impervious underwear, such as acrylic and nylon garments which trap sweat, and use of a drying powder may be helpful. Short term use of topical steroids for up to one month is useful for patients with dermatosis. Some patients with idiopathic pruritus ani respond favourably to such conservative management. Unfortunately, a significant percentage remains very difficult to treat and represents an important clinical challenge. Attempts to treat refractory pruritus ani include perianal injection of anaesthetic agents,14
surgical disruption of the sensory nerve supply to the perineal area,15
methylene blue injection,17
and even hypnotherapy.18
Most of these attempts have had limited success, and some have had significant side effects.
Capsaicin is a natural alkaloid extracted from red chili peppers. Its pharmacological action is mainly depletion of substance P from sensory neurones. Capsaicin binds specifically to type C sensory neurones, induces release of substance P, followed by inhibition of synthesis, transport, and storage of this neuropeptide.5
Topical capsaicin has been described as a safe and effective medicine for the relief of pain associated with postherpetic neuralgia, rheumatoid arthritis, and several other pain related conditions. It has also been shown that capsaicin is effective in the treatment of histamine induced pruritus, aquagenic pruritus, itching associated with uraemia, nodular prurigo, and pruritus related to postmastectomy syndrome.3
In the present study, only patients with chronic (longer than three months’ duration) intractable pruritus ani were included. Topical capsaicin cream in concentrations of 0.025%, 0.5%, and 1% had previously been used to treat itching in other pathologies.19
Although no serious side effects were reported, burning sensation at the site of application prevented its use in up to 30% of patients.20
As the perianal region is a very sensitive area of the body, we first conducted a preliminary investigation to establish the acceptable drug concentration. In this study, we found that a concentration of 0.006% capsaicin was effective in alleviating pruritus ani without the significant burning sensation associated with more concentrated preparations.
Our study demonstrated, for the first time, that capsaicin can be used successfully to treat chronic intractable pruritus ani. Patients in this study experienced dramatic itching relief after the first day of treatment. Itching was relieved in 31 of 44 patients in the treated group compared with one in the placebo group (p<0.0001). Overall, five of 49 patients (10%) dropped out of the study during the first week of capsaicin 0.006% application because of intolerable burning sensation (four patients) or urticaria (one patient). No other significant side effects or complications were noted. During the follow up period, the trial was conducted as an open label study and “responders” had stopped daily capsaicin applications. Although itching recurred sporadically in all patients, patients needed a mean application of capsaicin every 1.6 days (SD 1.2; range 0.5–7 days) to remain symptom free (or near symptom free).
A long term follow up study showed that the therapeutic effect of capsaicin did not decrease in general over time. However, two patients needed more frequent capsaicin applications and two patients more concentrated capsaicin preparations in order to remain symptom free in the long term follow up groups. Burning sensation was mild in two patients receiving capsaicin 0.012%. Burning sensation decreased in most patients over time and probably a more concentrated capsaicin preparation can be used in most patients, if required. Further studies are necessary to more precisely establish the range of effective capsaicin concentration for long term treatment. In the “responders” group, more patients were completely symptom free than nearly symptom free during the controlled phase compared with the follow up period. This was mainly due to the instructions given to the patients during the follow up period to apply capsaicin if symptoms recurred. Most of the patients who ignored this suggestion and applied capsaicin on a daily basis remained completely symptom free. Thus it is suggested to offer patients both possibilities and let them chose according to their preference.
In summary, perianal application of 0.006% capsaicin cream is a new and promising approach to the treatment of chronic idiopathic intractable pruritus ani. This drug concentration was significantly effective and safe in this pathology. The study also suggests that the neuropeptide substance P may play a key role as a mediator of itching in chronic pruritus ani.