| disease | Anal Cutaneous Pruritus |
| alias | PA, Pruritus Ani |
Anal cutaneous pruritus (pruritus ani, PA) is a common localized cutaneous pruritus. Mild itching may occasionally occur in the anal area, but if the cutaneous pruritus becomes severe and persistent, it develops into pruritus ani. It is a common localized neurofunctional skin disorder, typically confined to the perianal region, though it may sometimes spread to the perineum, vulva, or posterior scrotum. This condition predominantly affects middle-aged and elderly individuals between 20 and 40 years old, while it is less common in those under 20 and rarely occurs in children. Men are more frequently affected than women, and individuals who lead sedentary lifestyles are more prone to developing this cutaneous pruritus. Secondary cutaneous pruritus has identifiable causes and is easier to treat, whereas idiopathic or unexplained PA is difficult to cure and often recurs, accounting for approximately 50% of all cases.
bubble_chart Pathogenesis
Anal cutaneous pruritus is commonly seen in middle-aged individuals. In some cases, it may be a localized symptom of systemic cutaneous pruritus, which is more prevalent among the elderly. Localized anal cutaneous pruritus is often associated with or secondary to anorectal diseases. Local inflammation and congestion increase skin circulation and temperature, and since the gluteal region is an area where heat dissipation is difficult, excessive sweating and moisture can lead to discomfort and cutaneous pruritus. First-time sufferers often resort to washing with hot water or prolonged topical application of corticosteroids, which may temporarily relieve cutaneous pruritus. However, over time, this can create a vicious cycle of pruritus—adverse irritation—worsening pruritus, exacerbating local symptoms. A diet high in spicy foods can also trigger anal cutaneous pruritus. Poor hygiene habits, such as inadequate cleaning of the perianal and perineal areas, scratching or rubbing through clothing, can aggravate cutaneous pruritus. Improper clothing, such as tight or ill-fitting underwear made from unsuitable materials like certain synthetic fibers or thick, rough fabrics, can hinder sweat evaporation and cause friction, further inducing anal cutaneous pruritus. In children, anal cutaneous pruritus is most frequently caused by enterobiasis (pinworm infection). Female pinworms crawling out of the anus to lay eggs create mechanical irritation, leading to anal cutaneous pruritus.
bubble_chart Clinical ManifestationsPA can be divided into primary cutaneous pruritus and secondary cutaneous pruritus based on disease cause.
(1) Primary cutaneous pruritus
Primary cutaneous pruritus is not accompanied by primary skin lesions, with cutaneous pruritus being the main symptom.
(2) Secondary cutaneous pruritus
Secondary cutaneous pruritus arises from primary diseases and various skin diseases, accompanied by obvious specific skin lesions and primary lesions. Cutaneous pruritus is often a symptom of the primary lesion. Examples include anal fistula, anal eczema, condyloma, neurodermatitis, anorectal tumors, and pinworms, all of which can cause anal cutaneous pruritus, falling into this category.
Initially, anal cutaneous pruritus is mild, with no significant changes in the anal skin, mostly paroxysmal. In chronic patients, cutaneous pruritus is more severe, lasting longer, especially at night. Excessive scratching or mechanical stimulation causes hyperplasia, thickening, and roughness of the perianal skin, deepening of anal folds, and local scratch marks, blood crusts, and exudate. Fecal residue may remain in the folds, and in more severe cases, infection may occur, presenting with pustules or purulent discharge, redness, and swelling. The lesions can extend to the perineum, scrotum, female vulva, or even the skin of both buttocks. Clinical examinations may reveal internal hemorrhoids, external hemorrhoids, mixed hemorrhoids, or anal fistula, or laboratory tests may indicate diabetes, enterobiasis, or Candida albicans infection.
Based on a typical history of anal cutaneous pruritus combined with clinical symptoms and signs, the diagnosis of this condition is not difficult, but determining the disease cause is more challenging. Generally, if there is a primary lesion in the anal region, it is secondary cutaneous pruritus; otherwise, it is primary cutaneous pruritus. Additionally, a comprehensive physical examination should be conducted, along with targeted necessary laboratory tests, such as routine blood, urine, and stool tests, liver and kidney function tests, urine glucose, blood glucose, glucose tolerance tests, as well as biopsies and smears.
1. Treat the primary disease or complications such as hemorrhoids, anal fistula, enterobiasis, etc. Administer appropriate antibiotics or antimicrobial agents to treat concurrent infections.
2. Avoid inappropriate self-treatment. Many patients with anal cutaneous pruritus are reluctant to seek medical attention and resort to improper self-treatment, such as scalding with hot water, applying high-concentration corticosteroids or counterirritant drugs, or using crude homemade physiotherapy devices. These methods do more harm than good, providing only temporary relief from cutaneous pruritus while prolonging and exacerbating the condition over time. Patients should be advised to discontinue such practices.
3. Maintain hygiene and avoid or minimize the consumption of irritating foods, such as spicy dishes, strong tea, coffee beans, and hard liquor. Wear loose, well-fitting clothing, preferably with cotton undergarments.
4. For localized anal cutaneous pruritus, topical treatment should be the primary approach. Systemic medications such as corticosteroids, anti-inflammatory mediators, and various sedatives have no significant antipruritic effect on anal cutaneous pruritus but often carry numerous side effects or adverse impacts. These should be avoided unless there is a clear indication for their use.
5. For cases with only localized cutaneous pruritus and normal anal skin, cleanse and cold-compress the anal area with 4% boric acid solution. Adding ice to lower the water temperature to around 4–5°C enhances the effect. The patient should squat and apply gauze or absorbent cotton soaked in the cold solution to the anal area for immediate relief. Perform this twice daily (morning and evening) for about 5 minutes each time. After cold compressing, dry the area with a towel and apply ordinary talcum powder to keep it dry. Ointments are unsuitable for this type of anal cutaneous pruritus, as they hinder heat dissipation and increase sweating, which may trigger pruritus. Instead, use cooling and drying lotions, such as white lotion or calamine lotion.
7. Injection therapy: Inject medication subcutaneously or intradermally to disrupt sensory nerves, reducing local sensation and eliminating symptoms. Local injuries heal, and over 50% of cases achieve permanent cure. However, severe cutaneous pruritus cases may relapse, requiring repeat injections. The injected drugs not only damage sensory nerves but may also affect motor nerves, leading to varying degrees of sensory fecal incontinence and sphincter dysfunction, though these usually resolve over time.
⑴ Subcutaneous alcohol injection: Alcohol dissolves nerve myelin sheaths without injuring axons, causing sensory nerve endings to degenerate and the skin to lose sensation until nerves regenerate. Two injection methods are available: ① Zonal subcutaneous injection: Divide the perianal area into four zones, injecting one zone at a time. After skin disinfection, inject 5–10 ml of 1% or 2% procaine solution subcutaneously with a long needle, leaving the needle in place, then inject 5–10 ml of 95% alcohol evenly without leakage or tension. Avoid intradermal injection to prevent skin necrosis or sphincter paralysis. Apply heat post-injection and administer sedatives for pain relief. Repeat every 5–10 days until all four zones are treated. ② Multiple-site subcutaneous injection: After local anesthesia, use a fine needle to inject 3–10 ml of 95% alcohol subcutaneously at multiple sites (0.5 cm apart, 2–3 drops per site), avoiding intradermal or sphincter muscle injection.
⑵ Methylene blue intradermal injection: Inject 0.2% methylene blue solution into the perianal skin to eliminate the sensation of nerve endings and relieve cutaneous pruritus. The injection solution is prepared by dissolving 0.2g methylene blue and 0.5g procaine in 100ml of distilled water. Apply merbromin solution to the perianal skin, then use a fine needle to inject the solution intradermally around the anus, administering 3-4 drops per injection site until the entire pruritic area is covered. The total volume should not exceed 20ml. After injection, cover the anal area with sterile gauze and administer morphine or codeine for pain relief.
8. Surgical Therapy
For spontaneous cutaneous pruritus that does not improve after the aforementioned treatments or recurs multiple times, surgical therapy may be employed. The surgical methods include denervation of the perianal skin and excision of the perianal skin.
(1) Subcutaneous Incision: Make a semicircular incision on each side of the anus, 5 cm from the anal margin. Incise the subcutaneous fat and dissect the skin flap medially to expose the lower border of the external sphincter. Further dissect the skin from the internal sphincter up to the level of the anal valves within the anal canal. Then, separate the skin anterior and posterior to the anus from the deep tissues to allow communication between the wounds on both sides of the anus. Finally, dissect the outer edge of the incision outward by 1–2 cm, suture the skin flap back in place after hemostasis, and sometimes place a drain, covering it with a pressure dressing. Bowel preparation is required before the surgery, and bowel movements should be controlled for 3–4 days postoperatively. The outcomes vary among reports, with the majority achieving good results, though there are cases of recurrence, wound infection, and dehiscence.
(2) Excision and Suture: Make an incision along the anal margin from front to back, followed by a curved incision laterally to enclose the affected skin within the incisions. Connect the ends of the incisions and excise the crescent-shaped skin between the two incisions, then suture the wound. Repeat the same procedure on the opposite side. Excision of the skin can relieve cutaneous pruritus, but wound infection may occasionally occur.
