๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
PRURITUS IN SPECIFIC LOCATIONS
Scalp Pruritus
Skin disorders involving the scalp (e.g. seborrheic dermatitis, psoriasis, folliculitis, lichen planopilaris, dermatomyositis) may present with pruritus localized to this area. However, scalp pruritus also occurs in the absence of any objective changes including in the setting of neuropathic disorders (e.g. small-fiber neuropathy, postherpetic neuralgia) or psychogenic itch. Trigger factors should be avoided and any under-lying cause treated if possible. Topical corticosteroids and antipruritic agents have been employed with inconsistent efficacy.
Anogenital Pruritus
Pruritus ani
Pruritus localized to the anus and perianal skin occurs in 1%โ5% of the general population, with a maleโ:โfemale ratio of ~4โ:โ1. The onset is typically insidious, and symptoms may be present for weeks or years before patients seek medical attention.
Pruritus ani can be primary (idiopathic) or secondary in nature. Primary pruritus ani is defined as pruritus in the absence of any apparent cutaneous, anorectal, or colonic disorder; it accounts for 25%โ95% of reported cases, depending upon the series. Possible causes include dietary factors such as poor personal hygiene and psychiatric disorders. Secondary pruritus ani has an identifiable etiology such as chronic diarrhea, fecal incontinence/anal seepage, hemorrhoids, anal fissures or fistulas, rectal prolapse, primary cutaneous disorders (e.g. psoriasis, lichen sclerosus, seborrheic dermatitis, allergic contact dermatitis), sexually transmitted diseases, other infections, infestations (e.g. pinworms), previous radiation therapy or trauma, and neoplasms (e.g. anal cancer). Pruritus ani (as well as pruritus vulvae or scroti) can also be neuropathic in origin and be due to compression or irritation of lumbosacral nerves from prolapsed intervertebral discs, vertebral body fractures, or osteophytic processes.
Findings on physical examination range from normal-appearing skin or mild perianal erythema to severe irritation with crusting, lichenification, and erosion or ulceration. Histologically, a nonspecific, chronic dermatitis is usually seen, but specific dermatoses (e.g. lichen sclerosus) and neoplastic disorders (e.g. extramammary Paget disease) can be excluded.
Evaluation includes a thorough history, complete cutaneous and general physical examination, and psychiatric screening. The latter is of importance considering that anxiety and depression may be aggravating factors for pruritus ani. Patch testing should be considered to exclude allergic contact dermatitis. Rectosigmoidoscopy and/or colonoscopy may be necessary, especially in patients with recalcitrant pruritus ani, in order to detect underlying conditions ranging from hemorrhoids to cancer. The possibility of pinworm infection should be considered, particularly in affected children. In patients receiving chronic antibiotic therapy who have liquid stools with a pH of 8โ10, Lactobacillus replacement therapy is recommended.
While secondary pruritus ani usually improves with treatment of the underlying disorder, management of primary disease can be very challenging. Mild cases often respond to elimination of irritants and triggers, sitz baths (e.g. with astringents such as black tea), cool compresses, and meticulous hygiene using water-moistened, fragrancefree toilet paper or a bidet. The area is then dried with blotting or a fan, with avoidance of rubbing and alkaline soaps (see Ch. 153). Application of zinc oxide paste can help to protect the skin from further irritation and friction.
A mild corticosteroid cream (class 6 or 7) is often effective in controlling symptoms. However, with greater disease severity or the presence of lichenification, more potent topical corticosteroids and prolonged treatment may be required, raising the risk of cutaneous atrophy. Topical calcineurin inhibitors, including use on a rotational basis with topical corticosteroids, may be helpful when longer courses of therapy are necessary.
Pruritus vulvae and scroti
These common disorders, which may be incapacitating and emotionally disturbing, are solely psychogenic in only 1%โ10% of patients. Like pruritus ani, patients with pruritus of the vulva or scrotum typically complain of symptoms that are worse at night, and repeated rubbing or scratching leads to lichenification. The evaluation, differential diagnosis, and treatment options are similar to those for pruritus ani.
Acute pruritus of the vulva or scrotum is often related to infections such as candidiasis or scabies, but allergic or irritant contact dermatitis should also be considered. Chronic pruritus in these sites may be caused by dermatoses (e.g. psoriasis, atopic dermatitis, lichen sclerosus, lichen planus, LSC), malignancy (e.g. extramammary Paget disease, squamous cell carcinoma), or atrophic vulvovaginitis. Scrotal pruritus secondary to lumbosacral radiculopathy has also been described. In general, irritation of sensitive genital skin from cleansing and toilet habits needs to be addressed, as well as treatment of any identifiable underlying cause.