Infestation of the skin by Sarcoptes scabiei, or scabies mite, produces an intensely pruritic eruption. Symptoms manifest approximately 30 days following exposure to the organisms as a result of the host immune response to the mites and their excrement. Typically, history will elicit an encounter with another person, or with a new environment, approximately 4 to 6 weeks before the initiation of symptoms.
The main presenting feature is intense, intracTable pruritus, most noTable at night. In adults, the typical findings are slightly longitudinal erythematous or brown papules, predominantly on the lateral feet, wrists, ankles, and interdigital spaces of the fingers and toes. Involvement may be evident within the axillae, groin, and extensor extremities (Figure 252-3). The head and neck are characteristically spared. In immunocompromised hosts, or persons with significant psychiatric compromise, lesions may appear as thick, crusted, confluent plaques on the hands, feet, and scalp, with or without a generalized distribution. In such patients, the condition is termed crusted scabies.
Scabetic papules and burrows. [Reproduced with permission from Wolff KL, Johnson R, Suurmond R: Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed. © 2005, McGraw-Hill, New York.]
Sampling of a longitudinal burrow by scraping with a scalpel blade is typically most helpful in establishing the diagnosis. Light microscopy of the sample, which is transferred to a glass slide and covered with a drop of mineral oil followed by a coverslip, may reveal intact scabies organisms, ova, or excrement (see Figure 252-4). However, sensitivity of this test is limited, and a negative result does not rule out the diagnosis.
Arrow points to louse on the skin. [Reproduced with permission from Wolff KL, Johnson R, Suurmond R: Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed. © 2005, McGraw-Hill, New York.]
Treat with 5% permethrin cream (pregnancy category B), apply from the neck down, leave on for 12 hours, and then bathe with soap and water. Treatment should be repeated in a similar fashion in 1 week. Treat all resident family members and household and intimate contacts.
Lindane should be avoided in children and pregnant women secondary to neurotoxicity.
Oral ivermectin (pregnancy category C) is an alternative treatment to permethrin cream and is easier to administer; however, it may have a slightly lower cure rate.2 Ivermectin should be avoided in pregnant and lactating women.
Supportive care involves use of oral antihistamines and topical corticosteroids after use of the appropriate scabicidal agent. Patients should be told to expect resolution of symptoms gradually over 1 to 2 weeks, although pruritus can sometimes persist for several weeks. Return of new lesions after initial improvement signifies incomplete treatment or reinfestation.
Pediculosis pubis is infestation of the groin with Phthirus pubis. Rarely, the eyebrows, eyelashes, chest, or axillary hair may also be involved.
Close examination of the hair-bearing areas reveals multiple small flesh-colored or slightly reddish organisms grasping the hairs close to the skin surface (Figure 252-4). In severe infestations, small bluish-gray macules may be noted, called maculae caerulea. Secondary infection and excoriations may also be present. Diagnosis of pediculosis pubis in children should prompt evaluation for potential sexual abuse. Diagnosis is based on physical examination findings.
Treatment is the same as for scabies. Topical treatments should be applied liberally to all affected hair-bearing areas, including the perirectal hairs.3 Attempts to identify the source of the infestation are important because reexposure may continue to occur.
INFLAMMATORY AND REACTIVE CONDITIONS
Seborrheic dermatitis is one of the most common skin disorders. It most notably affects the scalp ("dandruff") and creases of the face and ears; however, other skinfolds, such as the intergluteal cleft, groin, axilla, inframammary folds, and umbilicus, can be affected (see chapters 250 and 251).
Seborrheic dermatitis of the scalp and skinfolds of the face presents as erythema with a greasy yellow scale (see Figure 250-4). When seborrheic dermatitis affects other skinfolds, erythema and maceration are evident (Figure 252-5).
Seborrheic dermatitis involving the diaper area of an infant. [Reproduced with permission from Wolff KL, Johnson R, Suurmond R: Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed. © 2005, McGraw-Hill, New York.]
Diagnosis is clinical and based on typical findings of seborrheic dermatitis on the face and scalp. By itself, groin or other skinfold involvement is hard to differentiate from the other inflammatory disorders such as cutaneous candidiasis, inverse psoriasis, allergic contact dermatitis, or streptococcal infection.
Treatment can relieve signs and symptoms, but there is no cure. The eruption will return after treatment ceases. Shampoos containing zinc pyrithione, selenium sulfide, salicylic acid, or tar preparations are used. Ketoconazole shampoo can be effective and is available by prescription (2%) or over the counter (1%). Hydrocortisone 1% cream can be used in mild cases, whereas hydrocortisone 2.5% cream or desonide cream or lotion may be required initially in more severe cases. Patients should be cautioned against long-term regular use of corticosteroids on facial or intertriginous skin, which may result in irreversible skin thinning and striae formation.
Intertrigo is an irritant dermatitis of the skinfolds resulting from moisture, heat, friction, and irritating substances like urine and feces. Intertrigo presents as erythema, maceration, and fissures in the occluded area of skinfolds, especially the groin and inframammary folds (Figure 252-6). Satellite papules and pustules are absent, and the affected areas are pruritic and may burn. Streptococcal superinfection should be considered if there is marked erythema and tenderness, especially in the extremes of age and the immunocompromised.
Intertrigo with possible streptococcal superinfection. [Reproduced with permission from Wolff KL, Johnson R, Suurmond R: Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, 5th ed. © 2005, McGraw-Hill, New York.]
Intertrigo is a diagnosis of exclusion (Table 252-1). Bacterial infection, especially with Streptococcus, is common. Differentiating cutaneous candidiasis from inflammatory intertrigo can be difficult. A diagnosis of cutaneous candidiasis is supported by the presence of satellite pustules and a positive potassium hydroxide examination. However, a negative potassium hydroxide examination does not exclude this possibility because yeast is difficult to obtain and visualize with this procedure. Scraping of peripheral scale or a pustule to send for fungal culture may help clarify the diagnosis.
Clinically, irritant dermatitis cannot always be distinguished from allergic contact dermatitis. A history should be taken to uncover any possible contact allergens or irritants such as neomycin-containing ointments, anesthetic creams, diphenhydramine cream, deodorants, feminine hygiene sprays, or other lotions, solutions, or home remedies.
Treat by keeping the affected areas dry and cool. All potential irritants should be avoided. Zinc oxide paste provides an excellent barrier to urine and fecal material.
For moist, weepy intertrigo, aluminum acetate (Burow solution) compresses can be used. Secondary bacterial infection should be treated with oral antibiotics with staphylococcal and streptococcal coverage. Topical antiyeast preparations, such as ketoconazole, may be helpful. If significant inflammation is present, a short course of 1% hydrocortisone cream or lotion may be helpful.
Hidradenitis suppurativa is an inflammatory condition, typically affecting the apocrine gland–bearing areas of the skin with recurrent, painful, draining nodules. The inciting event is follicular occlusion, prompting rupture of the follicular contents and resulting intense inflammation.4
Axillary and inguinal skin demonstrates varying numbers of inflammatory nodules, many of which may form connecting tracts, with resultant drainage onto the skin surface (Figure 252-7). Lesions may heal with characteristic icepick scarring, which may facilitate diagnosis.
Hidradenitis suppurativa involving the buttock region. [Photo contributed by University of North Carolina Department of Dermatology.]
Diagnosis is clinical. Treatment is clindamycin 1% lotion twice daily and use of antibacterial soaps, such as chlorhexidine, once to twice weekly. Incision and drainage should be minimized because it may increase scarring. Further systemic treatments, such as acitretin, finasteride, or prednisone, may work in some cases and are best coordinated by a specialist. In severe cases, systemic biologics or surgical excision of apocrine-bearing skin has been attempted.