Published on 18/03/2015 by admin
Filed under Dermatology
Last modified 22/04/2025
This article have been viewed 1380 times
William F.G. Tucker and James B. Powell
Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports
Scabies is a characteristically pruritic skin condition due to infestation by the itch mite Sarcoptes scabiei. Patients can be of any age or social strata, and personal hygiene is no guarantor of freedom from infection. It is endemic in many impoverished communities worldwide. Heavy parasitization results in crusted or ‘Norwegian scabies,’ and tends to occur in the elderly, mentally disadvantaged, immunocompromised, and those unable to scratch.
Lassa S, Campbell MJ, Bennett CE. Br J Dermat 2011; 164: 1329–34.
Those aged 10–19 years showed highest infestation rates with prevalence in females greater than in males. Prevalence dropped steadily from the 20–29 years age group but rose again in the 80+ group.
Infection with the scabies mite results from close personal contact with an infested individual, and generally requires prolonged skin-to-skin contact. Where heavily colonized, as in crusted scabies, clothing and surroundings can become sufficiently contaminated with live mites as to cause a significant hazard to their attendants and companions. The development of itching in close contacts/family members is almost pathognomonic.
Because newly infected patients do not begin to itch until 4 to 8 weeks after being infested, and may have little or no visible rash, the infestation is passed on easily and unintentionally. Once sensitized to the mite, re-infestation results in immediate symptoms. Equally, itching can continue for some weeks after mite cure. Secondary impetiginization is common in children.
Itching at night and when warm is a hallmark feature. Inflammatory papules and nodules often develop in genital areas, axillae, and around the nipples. In crusted scabies hyperkeratotic and crusted plaques can be seen.
Suspicion is the prerequisite for disease control and scabies infestation should come to mind in any patient with (unexplained) pruritus.
Total isolation from other people is clearly unnecessary with a causative organism that cannot jump or fly, and can survive for only approximately 72 hours away from the skin.
Topical application of antiscabetic agents is standard practice. Sulfur was the first effective agent and is still used in many countries, and when nothing else is suitable, as in very young infants. Benzoyl benzoate has been the mainstay of therapy, and is cheap and effective if used properly. It has an unfortunate tendency to cause eczematous rashes after repeat applications. Lindane (γ-benzene hexachloride) was in very widespread use until recently, and is very effective. Unfortunately, it accumulates in body fat stores and has been implicated in causing neurologic damage in infants; it has been withdrawn in the UK. Malathion is well tolerated and has the theoretic advantage of prolonged retention in the epidermis, so that re-infestation may be reduced. Permethrin as a 5% cream is easy to use, and has proven to be well tolerated and effective.
When deciding upon which antiscabetic to use, efficacy, cost, tolerability, resistance, and safety are important. Treatment regimens vary between products but the key to success is to ensure that adequate concentrations of the scabicide are in contact with the whole body for a sufficiently long period. It is generally accepted that the face and scalp do not need treatment except in infants and the immunocompromised individual. Reservoirs of infection include the subungual areas which must therefore be addressed when applying topical therapy. What is essential is that all intimates of the patient, whether apparently infected or not, are treated at about the same time. Many clinicians find an explanatory leaflet, detailing exactly how to apply a prescribed antiscabetic and also the need to launder clothes and bedding, helpful. The skills and patience of the physician are often rigorously tested throughout this process!
Ivermectin in single doses of 200 µg/kg has been shown to be very effective in a number of studies, although it is no more effective than properly applied permethrin. It is unlicensed for this indication in humans, but is used in animal ‘mange’ and is widely and safely used in onchocerciasis. Ivermectin should therefore be reserved for the treatment of crusted scabies and when appropriate application of topical antiscabetics is not possible, e.g., compliance, severe eczematization.
When treating crusted scabies combined topical and oral therapy may have to be considered to achieve a cure. Additional keratolytic therapy such as emollients, salicylic acid, and bathing may be needed to remove hyperkeratotic plaques.
Visualization of mites and burrows
The one specific investigation for scabies is to isolate the mite; nothing is more guaranteed to ensure compliance than to show a patient their co-dweller under the bench microscope. Dermatologists take great delight in capturing their quarry, and each will be an advocate of one particular method. With standard scabies, burrows are generally easiest to find around the hands, and the mite can often be seen as a dark dot at one end. A dermatoscope can help visualize the mite in situ and even reveal the characteristic triangle or ‘delta wing’ appearance at the mite’s head.
Argenziano G, Fabbrocini G, Delfino M. Arch Dermatol 1997; 133: 751–73.
With the aid of a blunt needle or sewing pin, the mite can be winkled out and placed on a glass slide. Note that hypodermic needles are useless for this purpose because they slice and shred the mite! Alternatively, the burrow is carefully scraped or shaved with a 15 Bard–Parker blade and the slice of stratum corneum placed on a glass slide with some immersion oil. Scraping/shaving is the test of choice in crusted scabies. Skin biopsy is often illuminating, particularly because the mite may be a surprise finding.
Yoshizumi J and Harada T. Clin and Exp Dermatol 2009; 34: 711–14.
The ‘wake sign’ reported here refers to the scale that may be seen at the edges of scabies burrows being reminiscent of the ‘wake’ left behind, somewhat momentarily, on the surface of water by an object moving through it, e.g., a ship.
The single most useful piece of portable diagnostic equipment is a fountain pen (or felt-tip pen/surgical marker, if none available) to allow one to conduct the ‘burrow ink test, as illustrated above’. A blob of ink is carefully applied to a suspected burrow, left for a minute or so, and wiped off with an isopropyl alcohol swab. If a burrow is present, then capillary action will have led to tracking of the ink into the burrow, leaving a wiggly line.
Woodley D, Saurat J H . J Am Acad Dermatol 1981; 4: 715–22.
Laboratory testing will frequently show a mild eosinophilia in peripheral blood. Scabies infestation can be difficult to diagnose clinically and can mimic a range of dermatoses. Serological investigations may in the future become more accurate and therefore useful in certain cases.
Jayaraj R, Hales B, Viberg L, Pizzuto S, Holt D, Rolland JM, et al. Diagn Microbiol Infect Dis 2011; 71: 403–7.
In this study specific IgE antibodies to a major scabies antigen were measured in 140 plasma samples from curently scabies infested and uninfested (control) subjects. Reported results showed 100% sensitivity and 93.75% specificity.
Taplin D, Meinking TL, Porcelain SL, Castillero PM, Chen JA. J Am Acad Dermatol 1986; 15: 995–1001.
Fifty-two patients in a rural community in Panama with microscopically confirmed mite presence in all but five were given a single head-to-toe application of either lindane 1% lotion or permethrin 5% cream. Microscopic confirmation of cure was sought at 2 and 4 weeks, with permethrin coming out ahead and curing 21 of 23 patients, compared to a cure rate of 15 of the 24 patients treated with lindane.
Hanna NF, Clay JC, Harris JRW. Br J Venereol Dis 1978; 54: 354.
An uncontrolled study using 0.5% malathion liquid in 30 patients, yielding an 83% cure rate at 4 weeks.
Gulati PV, Singh KP. Indian J Dermatol Venereol Leprol 1978; 44: 269–73.
One hundred and fifty-eight clinically diagnosed patients were randomly allocated to use either 25% benzyl benzoate emulsion or 5% sulfur ointment. Treatment was applied at least three times over 24 hours. The sulfur seems to have been marginally more effective.
Strong M, Johnstone PW. Cochrane Database Syst Rev 2007; 3: CD000320.
A new search for studies and content was performed in 2010, but no changes to the conclusions were made. Authors identified 22 small trials for inclusion (19 from resource-poor countries) containing 2676 patients in total. No herbal or traditional medicine trials were identified for inclusion. Permethrin was identified as the most effective topical treatment for scabies with ivermectin appearing to be an effective oral treatment. Authors state that more research is needed on effectiveness of malathion including in comparison to permethrin and in institutional and community settings.
Fatimata LY, Caumes E, Ndaw CAT, Ndiaye B and Mahe A. Bull WHO 2009; 87: 424–30.
In this study, which excluded those with crusted scabies, topical benzyl benzoate 12.5% was more effective than oral ivermectin in treating scabies infestation. Authors recommend a single application initially with a second used only in cases of treatment failure.
Avila-Romay A, Alvarez-Franco M, Ruiz-Maldonada R. Pediatr Dermatol 1991; 8: 64–6.
Readers will be pleased to learn that cold cream came out best, with no clinical failures at day 10 in the 26 patients (of 51) assigned to this arm of the trial.
Amer M, El-Gharib I. Int J Dermatol 1992; 31: 357–8.
Taplin D, Meinking TL, Chen JA, Sanchez R. Pediatr Dermatol 1990; 7: 67–73.
Both these studies show superior efficacy for permethrin, with clinical cures of 91 of 97 vs 72 of 97 patients. The study also measured parasitic cure, and by this outcome permethrin was much more effective, curing 42 of 47 vs 28 of 47.
Macotela-Ruiz E, Pena-Gonzalez G. Gac Med Mex 1993; 129: 201–5.
This randomized trial compared the treatment of 55 patients with a clinical diagnosis of scabies with either a single dose of ivermectin 200 µg/kg or placebo. After 7 days the code was broken because there was such a significant improvement in the treated group: 23 of 29 vs four of 26.
Glaziou P, Cartel JL, Alzieu P, Briot C, Moulia-Pelat JP, Martin PM. Trop Med Parasitol 1993; 44: 331–2.
A randomized study in French Polynesia comparing a single dose of 100 µg/kg ivermectin with 10% benzyl benzoate lotion applied below the neck and repeated 12 hours later. Both were equally effective.
Offidani A, Cellini A, Simonetti O, Fumelli C. Eur J Dermatol 1999; 9: 100–1.
Six patients with heavy mite infestation received a single dose of 200 µg/kg ivermectin. All were clinically cured.
Nofal A. J Eur Acad Dermatol Venereol 2009; 23: 793–7.
These patients initially received a single dose of ivermectin (200 µg /kg). After 2 weeks two patients were completely cured and the other six who remained infested received a second dose of ivermectin. Two weeks later this had cured a further four patients but two remained infested and required a further dose of ivermectin combined with permethrin 5% and salicylic acid 5% to achieve cure.
Usha V, Gopalakrishnan Nair TV. J Am Acad Dermatol 2000; 42: 236–40.
In this trial in 88 patients, permethrin came out better for cure at 2 weeks.
Pacque M, Munoz B, Greene BM, White AT, Dukuly Z, Taylor HR. Lancet 1990; 335: 1377–80.
De Sole G, Remme J, Awadzi K, Accorsi S, Alley ES, Ba O, et al. J WHO 1989; 67: 707–19.
In both studies ivermectin was remarkably well tolerated, even in repeated courses.
Barkwell R, Shields S. Lancet 1997; 349: 1144–5.
This is the only ‘fly in the ointment’ with ivermectin: the authors report on the treatment of 47 elderly, mentally disadvantaged residents of an institution with a single dose of ivermectin at 150–200 µg/kg body weight. All had failed to respond to multiple earlier courses of lindane and crotamiton. All were cured, but over the next 6 months 15 died from a number of causes, whereas only five died in an equivalent, matched population within the same unit. Many patients were taking other drugs, raising the possibility of interactions.
Gordon RM, Davey TH, Unsworth K, Hellier FF, Parry SC, Alexander JB. Br Med J 1944; 2: 803–6.
A bath a day for 6 days using 20% tetmosol soap cured all six patients; three baths on alternate days cured 88 of 110 patients.
Presumably the limiting factor in wartime Britain was the lack of hot bathwater!
Mellanby K. Br Med J 1945; 1: 38–9.
A non-randomized open study carried out in a large mental hospital showed significant reductions in infection rates.
Where has this soap gone?
Hernandez-Perez E. Arch Dermatol 1976; 112: 1400–1.
Forty patients with scabies were treated with a single external application of a 10% suspension of thiabendazole. Thirty-two (80%) seemed to be cleared, but six needed a second course.
Perhaps worth trying when patients have had adverse reactions to other topical agents.
Shashindran CH, Gandhi IS, Lal S. Br J Dermatol 1979; 100: 483.
Unlike pediculosis, where there is some evidence of benefit, this did not seem to work. The potential toxicity of co-trimoxazole is also of concern.
Amerio P, Capizzi R, Milan M. Eur J Dermatol 2003; 13: 69–71.
Forty patients received either 5% permethrin cream or a foam formulation of 0.16% pyrethrins synergized with piperonil butoxide, designed for head and pubic lice. It was equally effective and, significantly, easy to apply.
Treatment of Skin Disease Comprehensive Therapeutic Strategies 4e
WhatsApp us
Permethrin 5% cream
Malathion 0.5% lotion
Benzyl benzoate
Lindane
Sulfur
Crotamiton
Ivermectin
Monosulfiram soap
Topical thiabendazole solution
Co-trimoxazole
Natural pyrethins
