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30/12/2015 Scabieshttp://www.uptodate.com/contents/scabies?topicKey=DERM%2F4038&elapsedTimeMs=11&source=search_result&searchTerm=scabies&selectedTitle=1%… 1/46 Official reprint from UpToDate www.uptodate.com ©2015 UpToDate Authors Beth G Goldstein, MD Adam O Goldstein, MD, MPH Section Editors Robert P Dellavalle, MD, PhD,MSPHMoise L Levy, MDTed Rosen, MD Deputy Editor Abena O Ofori, MD Scabies All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Nov 2015. | This topic last updated: May 21, 2015. INTRODUCTION — Scabies ( the itch ) is an infestation of the skin by the mite Sarcoptes scabiei that results inan intensely pruritic eruption with a characteristic distribution pattern. EPIDEMIOLOGY — The incidence of scabies undergoes cyclical fluctuations on a worldwide basis, although allparts of the globe are not necessarily in the same phase of the cycle at the same time. In the 1960s the incidencein Europe and North America began to increase, and by 1980 had reached near-pandemic levels. Since then, therate of scabies has declined somewhat, but the disease is still common. As many as 300 million people may beaffected worldwide [1 ].Crowded conditions increase the prevalence of scabies in the population, and scabies can occur in epidemics ininstitutional settings [1]. In temperate climates, scabies is more common in the winter than the summer probablydue to both greater physical crowding in the winter and because mites can survive longer on fomites in colder temperatures [1]. TRANSMISSION — Transmission of scabies is usually from person to person by direct contact [2]. Transmission from parents to children, and especially from mother to infant, is routine. Schools do not ordinarily provide the levelof contact necessary for transmission. In young adults, the mode of transmission is usually sexual contact.In typical conditions, mites can survive off a host for 24 to 36 hours [3]. They can survive much longer in colder conditions with high relative humidity [3,4]. Under comparable conditions, female mites (which burrow into the skinand cause disease) survive longer than their male counterparts [4]. Although uncommon, there have been many authenticated instances in which scabies was contracted by wearingor handling heavily contaminated clothing, or by sleeping in an unchanged bed recently occupied by an infestedindividual. Transmission through clothing or linens is more likely with higher parasite burdens as seen in crusted(Norwegian) scabies [1,5]. Animals can also contract scabies, but the subspecies that infect cats and dogs are distinct from those infecting humans. While cross-species transmission can occur, scabies contracted from a cat or dog is unlikely to cause extensive infestations on a human host unless the animal does not receive treatment. These mites do not usuallyreproduce on human hosts and rarely live longer than a few days [5]. They are not normally transmitted from onehuman host to another [6]. MORPHOLOGY AND HABITS — Sarcoptes scabiei, var. hominis is a whitish-brown eight-legged mite, shapedmuch like a turtle (picture 1A). The female, which causes the clinical manifestations, is approximately 0.4 x 0.3mm. This is at the border of visibility with the naked eye [1,5], and the burrowing habits of the parasite prevent itfrom being observed by patients. Burrowing is facilitated by secretion of proteolytic enzymes that causekeratinocytic damage detectable at the ultramicroscopic level [7].When fertilized, the female burrows quickly into the epidermis to the level of the stratum granulosum, where itextends its burrow by approximately 2 mm each day, lays two or three eggs at a time to a total of 10 to 25, anddies in place after one to two months. Larvae hatch in three to four days, molt three times, leave the burrow for the ®® 30/12/2015 Scabieshttp://www.uptodate.com/contents/scabies?topicKey=DERM%2F4038&elapsedTimeMs=11&source=search_result&searchTerm=scabies&selectedTitle=1%… 2/46 surface, copulate, and continue the cycle. At any one time, typical patients harbor an average of 10 to 15 mitesduring an initial episode, and about half as many with subsequent infestations [8,9]. CLINICAL MANIFESTATIONS — The prominent clinical feature of scabies is itching. It is often severe andusually worse at night. The pruritus is the result of a delayed type-IV hypersensitivity reaction to the mite, mitefeces, and mite eggs [8]. Incubation period — Symptoms of scabies typically begin three to six weeks after primary infestation [10-12].However, in patients who have previously been infested with scabies, symptoms usually begin within one to threedays after reinfestation, presumably because of prior sensitization of the patient's immune system [10,11,13]. Typical infestation — The essential lesion is a small, erythematous, nondescript papule, often excoriated andtipped with hemorrhagic crusts (picture 2A-B). It is not a dramatic lesion and not always easy to see. Morestriking, when present, is the burrow. Pathognomonic when correctly identified, the burrow is a thin, grayish,reddish, or brownish line that is 2 to 15 mm long (picture 3A-B). Burrows are often absent, however, or obscuredby excoriation or secondary infection. Miniature wheals, vesicles, pustules, and rarely bullae may also be present.The distribution of scabies usually involves the sides and webs of the fingers (picture 4A-B), the flexor aspects of the wrists (picture 2A), the extensor aspects of the elbows, anterior and posterior axillary folds (picture 5), the skin immediately adjacent to the nipples (especially in women), the periumbilical areas, waist, male genitalia (scrotum,penile shaft, and glans) (picture 6), the extensor surface of the knees, the lower half of the buttocks and adjacentthighs, and the lateral and posterior aspects of the feet (figure 1). The back is relatively free of involvement, andthe head is spared except in very young children. Rarely, scabies may be localized to a single area [14,15 ].Patients occasionally develop a nodular form of scabies, exhibiting firm, erythematous, extremely pruritic, dome-shaped lesions, 5 or 6 mm in diameter. The groin, genitalia, buttocks, and axillary folds are the usual sites of involvement (picture 7A-B). Patients can develop generalized urticaria with scabies, and there are case reports of patients presenting with urticaria as the initial manifestation of scabies [16,17].Young children and infants often show heavy involvement of the palms and soles and all aspects of the fingers,and may even show evidence of mites under the nail plates (picture 8A-C). Lesions in children are usually moreinflammatory than in adults and often are vesicular or bullous (picture 9A-E).Secondary staphylococcal infections, including impetigo, ecthyma, paronychia, and furunculosis, frequentlycomplicate the picture, especially in the summer months. In addition, constant scratching and the application of irritating or sensitizing proprietary medications may result in extensive eczematization. (See Skin abscesses,furuncles, and carbuncles .) Crusted scabies — In most patients, after an initial exponential increase in mites and lesions in the early weeksof infestation, the numbers of both decline. Healthy patients with established scabies generally harbor fewer thanone hundred mites. The reduction is largely a function of host cellular immunity.Crusted scabies (Scabies crustosa, Norwegian scabies, keratotic scabies) can occur in the presence of AIDS,leprosy, lymphoma, and other conditions and treatments that compromise cellular immunity [18]. This special formis sometimes also seen in older adults and in patients with Down syndrome [19]. (See Fever and rash in HIV- infected patients , section on 'Scabies'.) The fissures associated with crusted scabies provide a portal of entry for bacteria. This may lead to sepsis as a complication of crusted scabies in older adults and immunocompromisedpatients [20 ].Crusted scabies begins with poorly defined erythematous patches that quickly develop a prominent scale (picture10A-C). Any area may be affected, but the scalp, hands, and feet are particularly susceptible. If untreated, thedisease usually spreads inexorably and may eventually involve the entire integument. Scales become warty,especially over bony prominences. Crusts and fissures appear. The lesions are malodorous. Crusts and scales areteeming with mites that number in the hundreds of thousands. Nails are often thickened, discolored, anddystrophic. Itching may be minimal or absent. 30/12/2015 Scabieshttp://www.uptodate.com/contents/scabies?topicKey=DERM%2F4038&elapsedTimeMs=11&source=search_result&searchTerm=scabies&selectedTitle=1%… 3/46 DIAGNOSIS — The diagnosis of scabies is generally made from the history and the distribution of lesions. Theexaminer should suspect the possibility of scabies in patients with one or more of the following [21,22]:Burrows are not always evident on clinical exam, but when seen, they increase the certainty of the diagnosis(picture 2B, 10C). Diagnostic tests such as skin scraping, dermoscopy, and the adhesive tape test can providemore definitive confirmation of the diagnosis, but negative results do not exclude scabies [1,23,24 ]. Thus, atherapeutic trial with an anti-scabietic medication may be helpful in difficult cases.Descriptions of the diagnostic tests for scabies are provided below. Skin scraping — In adults, areas most likely to yield mites are between the fingers, sides of hands, wrists,elbows, axillae, groin, breasts, and feet. Sites on the palms, soles, or torso may offer the highest yield in infantsand young children. The following procedure allows identification of mites or eggs in scrapings from burrows or papules [25]:In cases of crusted scabies, large numbers of mites and eggs may be seen on skin scraping (picture 11) [19 ]. Dermoscopy — Dermoscopy (examination of the skin surface with a handheld dermatoscope to allowvisualization of specific structures related to the epidermis, the dermal-epidermal junction, and the papillary dermis)may be a useful tool in scabies [23,24]. The test can be used to directly visualize mites and eggs for diagnosis or to guide the placement of skin scrapings [26].The characteristic finding on dermoscopic examination is a dark, triangular shape that represents the head of themite within a burrow ( delta wing sign) (picture 12A-B). Eggs may also be visible. Of note, these features arefrequently difficult or impossible to detect in patients with dark skin [23 ].Due to the need for specialized equipment and proper training, the use of dermoscopy remains primarily limited todermatologists. Adhesive tape test — The adhesive tape test for scabies involves the use of transparent tape with a strongadhesive (eg, clear packing tape) [23,27]. The tape is firmly applied directly to a skin lesion and then is rapidlyWidespread itching that is worse at night, spares the head (except in infants and young children), and seemsto be out of proportion to visible changes in the skin● A pruritic eruption with characteristic lesions and distribution (figure 1)● Other household members with similar symptoms● Assemble the necessary equipment (alcohol preparation, mineral oil, fountain pen, number 15 blade, glassslide and coverslip, microscope).●Look for a non-excoriated papule with a fine white to gray line across the top. Utilization of the following inktest facilitates the correct identification of a burrow, and is a helpful adjunct to the skin scraping procedure:●Place two or three drops of ink over the papule. Leave the ink on for 5 to 10 seconds, then wipe thearea clean with an alcohol prep. The ink will seep into the burrow, and a fine stained line will be evident.ãPlace a drop of mineral oil on the skin lesion, and either scrape the area with a number 15 blade or pinch thearea between the thumb and index finger and superficially shave the top layer of skin. Anesthesia is notnecessary.●Place the specimen on a glass slide, apply the coverslip, and examine it under the microscope at 10xmagnification to identify the female adult mite (0.4 mm long), the male (0.2 mm long), the eggs, or feces(picture 1A-B).●Mite eggs are all the same size (picture 1A-B), while air bubbles are different sizes and change withcompression of the slide.● 30/12/2015 Scabieshttp://www.uptodate.com/contents/scabies?topicKey=DERM%2F4038&elapsedTimeMs=11&source=search_result&searchTerm=scabies&selectedTitle=1%… 4/46 pulled off. After applying the tape to a glass slide, the clinician utilizes a microscope to examine the tape for mitesand eggs. An advantage of the adhesive tape test is the lack of need for specialized equipment (other than a microscope).The procedure may also be useful in children who cannot tolerate skin scrapings. Test selection — All of the tests above can be used to successfully diagnose scabies [23,24]. Pending additionalcomparative data, clinician skill, patient tolerance, and equipment availability remain the main factors thatdetermine the selection of an appropriate diagnostic test. DIFFERENTIAL DIAGNOSIS — The lesions of scabies are often excoriated, obscuring their appearance. Thedifferential diagnosis is broad and scabies can appear similar to eczema, tinea, atopic dermatitis, Langerhans cellhistiocytosis (picture 13A-B), systemic lupus, bullous pemphigoid, papular urticaria, seborrheic dermatitis, andacropustulosis of infancy (picture 14) [5]. As discussed above, the diagnosis of scabies usually rests on the typical distribution of lesions and a history of affected family members. TREATMENTEradication of mites — There are relatively few well-designed trials comparing treatments for scabies [28 ].Considering the toxicity and efficacy of various therapies, topical permethrin 5% cream and oral ivermectin are reasonable first-line therapies. Other topical treatments for scabies include benzyl benzoate (not available in theUnited States), crotamiton, lindane, malathion, and sulfur in petrolatum [1,5,29 ].Good timing and adequate communication are essential to the success of scabies treatment. Household and closepersonal contacts must be treated simultaneously to prevent recurrent infestation. (See 'Control of transmission'below.) Permethrin — A systematic review found heterogeneity of results among five trials comparing topicalpermethrin with topical lindane, leaving some uncertainty about the relative effectiveness of the two agents [28]. The largest such trial in 467 patients found similar clinical cure rates 28 days after a single whole-body applicationof 5% permethrin cream or 1% lindane lotion (91 versus 86 percent) [30]. Permethrin has less neurotoxicity than lindane, particularly in children, and is therefore preferred. Permethrin is classified as category B for use inpregnancy (table 1).Patients should massage permethrin cream thoroughly into the skin from the neck to the soles of the feet,including areas under the fingernails and toenails. Thirty grams is usually sufficient for an average adult. Thehairline, neck, temples, and forehead may be infested in infants and geriatric patients. In these populations,permethrin should also be applied to the scalp and face, sparing the eyes and mouth.The cream should be removed by washing (shower or bath) after 8 to 14 hours. Although the relative efficacy of one versus two applications of permethrin has not been formally studied, a second application one to two weekslater has been recommended [8,31 ].Permethrin 5% cream appears to be safe and effective even when applied to infants less than one month of ageinfected with neonatal scabies. Cotton mitts or socks on the hands of infants and young children at bedtime willprevent them from rubbing the cream into their eyes. Treatment of infants is discussed in detail separately. (See Vesiculobullous and pustular lesions in the newborn , section on 'Scabies'.) Oral ivermectin — Oral ivermectin, an anthelmintic with a half-life of 36 hours, can also successfully treatscabies [32-36 ]. One study found a much higher cure rate at seven days with single-dose ivermectin 200 mcg/kgthan placebo (79 versus 16 percent) [37].Randomized trials have suggested that a single dose of ivermectin 200 mcg/kg is as or more effective than asingle application of 1% lindane [38,39], but less effective than a single application of permethrin [32]. Two doses of ivermectin achieved equivalent cure rates to a single application of permethrin [32].
