Clinical pearls: A 37-year-old man with a rash. . .

Chief Complaint. “Rash.”

History of Present Illness. This 37-year-old man presented to the emergency department (ED) with a chief complaint of “rash” that he believed to be psoriasis. Three weeks prior, he had developed intensely pruritic, erythematous, scaly patches on his hands and abdomen, which eventually coalesced over his trunk, back, neck, groin, and extremities (Figure 1). He described the episode as being like previous episodes. When this episode began, he had applied clobetasol propionate (Temovate) cream, but discontinued its use secondary to severe burning pain. He experienced limited relief from pruritus with triamcinolone ointment and Aveeno baths. The patient’s dermatologist had retired the year before, and the patient was unsuccessful in arranging an appointment with another specialist. On arrival to the ED, the patient complained of diffuse, severe pruritus that limited his ability to sleep, but denied fevers or other systemic symptoms. None of the patient’s acquaintances had a similar rash.

Past Medical History. Past medical history was notable for the acquired immunodeficiency syndrome (AIDS) and a CD4+ count of 207 cells per cubic millimeter (nadir 15 cells/mm^sup 3^). Viral load was unknown at the time. The patient reported compliance with antiretroviral medications. Over the past three years, he had also been treated for psoriasis with topical triamcinolone ointment, achieving intermittent success.

Physical Examination. The patient was afebrile, blood pressure was 134/78 mm Hg, pulse 87 beats/min, respiratory rate 16 breaths/ min, and oxygen satura-tion 99% on room air. The patient was alert and oriented. Skin examination was notable for diffuse, erythematous, macerated scale over the trunk, abdomen, neck, and extremities-including the hands and feet. On close examination, tiny black specks were diffusely present. Areas around the waistline were excoriated and open (Figure 1).

Head, eyes, ears, nose, and throat examinations were otherwise normal. There was no evidence of thrush. The lungs were clear bilaterally. Cardiac examination was normal and without murmurs. The abdomen was soft, without distention. Bowel sounds were normal. There was no tenderness to deep palpation, though excoriated areas of skin around the waistline were tender to palpation. The extremeties had no edema. Musculoskeletal and neurological examinations were unremarkable.

Laboratory. Scrapings were performed in the ED. The preparation was positive for adult mites, eggs, immature mites, and feces of the species Sarcoptes hominis (Figure 2). Fungal preparation was negative.

Figure 1. Front view (above) and back view (next page) of the patient on presentation to the emergency department.

Figure 1. Front view (above) and back view (next page) of the patient on presentation to the emergency department.

Diagnosis. Crusted (Norwegian) scabies.

Follow-up. The patient was treated with ivermectin 18 mg (200 [mu]g/4 mg) orally in the ED and 18 mg to be taken two weeks later. Hydroxyzine HCl 50 mg, every six hours, was prescribed for pruritus, and follow-up with dermatology was arranged. Anyone with direct skin contact with the patient, his clothes, or bed linens was treated with permethrin 5% cream over the entire body once a week for two weeks. Complete resolution of skin lesions was noted at follow-up in the dermatology clinic.

Discussion. Scabies is an infestation of the epidermis by the mite Sarcoptes scabiei var. hominis, an obligate human parasite. The mite is about 0.5 mm in length. It burrows tunnels into the epidermis, depositing feces along the way. The female also lays eggs in the tunnel she creates. The infestation has been described for more than 2,500 years. It was mentioned by Aristotle and was referred to in several manuscripts during the first millennium. A mite was first identified as the etiology of localized scabies by Bonomo in the late 1600s, and in 1848, Danielssen and Boeck described a diffuse, crusted form of the disease in a series of Norwegian patients with Hansen’s disease.1,2 Generalized scabies has formerly been referred to as Norwegian scabies. However, as there is no association between this form of scabies and Norway, the term “crusted scabies” is now preferred.

Figure 2. The mites of the species Sarcoptes hominis. A, adult mite (S. scabiei var. hominis). B, adult mite and egg. C, immature mites.

There are approximately 300 million cases of scabies in the world annually.3 Infestation follows a cyclical pattern in the Western world, while in tropical regions it is endemic.4 The prevalence is about 100% in some areas of Central and South America, and in parts of Bangladesh the number of children with “the itch” exceeds the numbers with diarrheal and respiratory diseases combined.5

Two forms of scabies can occur. In localized, or classic scabies, infestation is limited with only about a dozen female mites per case. Pruritus, however, may be intense.6 The incubation period in adults is usually three weeks, but may be longer. Reinfestation, however, provokes immediate (1-3 days) symptoms. Mites burrowing within the epidermis leave gray or skin-colored ridges that are visible to the naked eye. The lesions usually affect the interdigital web spaces of the hands, the flexor surfaces of the wrists and elbows, the axilla, the genitalia, and under the breasts of women. Burrows are typically 0.5-1.0 cm in length with a white papule at one end. On light-skinned individuals, brown or black specks may be seen representing fecal scybala. Skin lesions may also be the result of immediate or delayed hypersensitivity reactions leading to an eczematous dermatitis, or may be due to excoriation from repeated scratching. This, in turn, may be complicated by cellulitis or impetigo.

In crusted scabies, a relatively rare form of the infestation, the disease results in marked hyperkeratosis and an erythematous, scaling eruption of the face, neck, scalp, extremities, and trunk. Up to 4,700 mites per gram of skin have been counted in hyperkeratotic patients, so there may be millions of mites infesting the epidermis of an affected individual.7 Crusted scabies is highly contagious, especially for health care workers. Nosocomial infections have been reported.8 In one report, 29 of 50 direct and indirect contacts of a patient with crusted scabies acquired the mite.9 Crusted scabies is associated with immunocompromised individuals and has been well documented in patients with HIV and HTLV-1 infections, organ transplant recipients, and those receiving topical or systemic glucocorticoid therapy. It is also associated with developmentally delayed and physically incapacitated individuals, patients with Down’s syndrome, and those with other neurologic disorders. Interestingly, crusted scabies is common in Aborigines in all regions of rural Australia, although there is no known or identified immunosupression.5

Crusted scabies is often misdiagnosed. It has been confused with eczema, psoriasis, ichthyosis, and adverse drug reactions.2,6,10 The differential diagnosis also includes seborrheic dermatitis, erythroderma, and Langerhans-cell histiocytosis.6

Definitive diagnosis of crusted scabies by microscopic examination can be made in the ED. A drop of mineral oil is placed over the burrow and the superficial scale is scraped with a scalpel blade. The sample is placed on a microscope slide and examined for the presence of adult mites, their eggs, or their fecal pellets (scybala).6 Serum analysis is unnecessary, although eosinophilia may be noted. Classic scabies may be more difficult to diagnose given the lower burden of parasites. Dermatoscopy and DNA amplification by polymerase chain reaction (PCR) followed by enzyme-linked immunosorbent assay (ELISA) are tools also used by some dermatologists in tertiary centers.11 However, these methods are not readily available in the ED or in many dermatology departments. A negative microscopic examination in classic scabies does not rule out infestation and, in the appropriate clinical setting, patients may still be treated with the response to topical scabicide noted in follow-up.

Lesions may remain indefinitely if not appropriately treated. Treatment is primarily with topical scabicides. Lindane (gamma- benzene hexachloride) 1% is applied thinly to all involved areas from the neck down and washed off after eight hours.6 Lindane is neurotoxic and can cause seizures, and it is not recommended in children under 5 years old, in pregnancy, or in lactation. It should also be avoided in patients with extensive dermatitis and should not be used after bathing as it has been known to cause seizures in these settings.6 Permethrin cream 5% is also effective and safe and should be applied in a similar manner to Lindane. It carries no associated risks of seizures. Single application of scabicide kills 90-95% of mites, so repeated administration is recommended.6

In immunocompromised or incapacitated individuals, topical application may not achieve total eradication of the mites even after repeated administration. If topical treatment is not likely to be effective or tolerated, ivermectin 200 [mu]g/kg may be given orally.12 Ivermectin interrupts GABA (gamma-aminobutyric acid)- induced neurotransmission in peripheral muscles of many parasites (note that in mammals GABA-mediated nerves occur only in the central nervous system). It is commonly used as prophylax\is against the heartworm Dirofilaria immitis in dogs.5,13,14 Single-dose therapy has been shown to be effective for eradicating uncomplicated scabies. However, immunocompromised patients, and those with more severely crusted forms of the disease, may require repeat dosing. In one study, eight of 11 of patients with HIV were cured following a single dose of ivermectin. Two were cured after an additional dose, and the one remaining patient required three doses and the application of permethrin. Recent literature suggests that ivermectin in combination with an additional scabicide is more effective than ivermectin alone in the immunocompromised.15 Ivermectin has been associated with idiosyncratic reactions and there is a concern, which is presently unconfirmed, about an increase in the death rate among residents in a long-term care facility after its use.15

Additional agents may be helpful in the treatment of scabies. Benzyl benzoate, sulfiram 25% solution, crotamiton 10% cream, and malathion have been used as scabicides. Antihistamines are an important ad-junct for pruritus. As noted above, crusted scabies is highly contagious and prophylaxis with a single application of a topical scabicide is recommended for anyone who comes in direct contact with a patient who has scabies or with the patient’s clothes or linens. Clothes and linens can be decontaminated by washing at 60 degrees Centigrade.

Clinical Pearls.

1. Immunocompromised patients, as well as those with psychological and neurological disease, are at risk for crusted scabies.

2. Crusted scabies differs from uncomplicated scabies in several ways that may confound diagnosis. The incubation period may be atypically brief, rash is commonly diffuse and may be non-pruritic, burrows may be obscured by thick scale, excoriation and super- infection may alter physical findings, and rash may not have responded to traditional therapy.

3. Microscopic diagnosis is achievable in the ED. Scraping is performed by applying a drop of mineral oil over a burrow or highly affected area, removing superficial scale with a scalpel blade, and examining for the presence of adult mites, their eggs, or their fecal pellets (scybala).

4. Systemic ivermectin (200 [mu]g/kg po) is an acceptable alternative treatment for patients unlikely to tolerate topical scabicides.

5. Prophylaxis is recommended for anyone who conies in direct contact with patients who have crusted (or uncomplicated) scabies or items that may be infested. This applies to health care workers and family members. Physicians should counsel patients with scabies to avoid contact with others who may be immunocompromised.

References

1. Ramos-e-Silva M. Giovan Cosimo Bonomo (1663-1696): discoverer of the etiology of scabies. Int J Dermatol. 1998; 37:625-30.

2. Gach JE, Headgerty A. Crusted scabies looking like psoriasis. Lancet. 2000; 356:650.

3. Orkin M. Scabies: what’s new? Curr Probl Dermatol. 1995; 22:105-11.

4. Downs AMR, Harvey I, Kennedy CTC. The epidemiology of head lice and scabies in the UK. Epidemiol Infect. 1999; 122:471-7.

5. Chosidow O. Scabies and pediculosis. Lancet. 2000; 355:819- 26.

6. Fitzpatrick TB, Johnson TB, Wolff K, Polano MK, Suurmond D. Color Atlas and Synopsis of Clinical Dermatology, Common and Serious Diseases. Third Edition. New York: McGraw Hill, 1997.

7. Walton SF, McBroom J, Mathews JD, Kemp DJ, Currie BJ. Crusted scabies: a molecular analysis of Sarcoptes scabiei variety hominis populations from patients with repeated infestations. Clin Infect Dis. 1999; 29:1226-30.

8. Chan LY, Tang WY, ho HH, Lo KK. Crusted (Norwegian) scabies in two old-age home residents. Hong Kong Med J. 2000; 6:428-30.

9. Hsueh PR, Lin BH, Hwang CC, Hsieh BL, Liu JC, Lin M. Nosocomial outbreak of scabies. J Formos Med Assoc. 1992; 91:228- 32.

10. Almond DS, Green CJ, Geurin DM, Evans S. Lesson of the week: Norwegian scabies misdiagnosed as an adverse drug reaction. BMJ. 2000; 320:35-6.

11. Bezold G, Lange M, Schiener R, et al. Hidden scabies: diagnosis by polymerase chain reaction. Bri Dermatol. 2001; 144:614- 8.

12. Meinking T, Taplin D, Herminda JL, Pardo R, Kerdel F. The treatment of scabies with ivermectin. N Engl J Med. 1995; 333:26- 30.

13. Campbell WC. Ivermectin: an update. Parasitol Today. 1985; 1(1):10-6.

14. Elmogy M, Fayed H, Marzok H, Rashad A. Oral ivermectin in the treatment of scabies. Int J Dermatol. 1999; 38:926-30.

15. Alberici F, Pagani L, Ratti G, Viale P. Ivermectin alone or in combination with benzyl benzoate in the treatment of human immunodeficiency virus-associated scabies. Br J Dermatol. 2000; 142:969-72.

Christopher Kabrhel, MD, William Binder, MD

From the Harvard Affiliated Emergency Medicine Residency, Brigham and Women’s Hospital/Massachusetts General Hospital (CK), and the Division of Emergency Medicine, Massachusetts General Hospital (WB), Boston, MA.

Received November 22, 2002; accepted December 9, 2002.

Section editor: Michelle H. Biros, MS, MD, Department of Emergency Medicine, Hennepin County Medical Center, Minneapolis, MN.

Photographer: John M. Williams, MD, PhD, Resident, Department of Dermatology, Massachusetts General Hospital, Boston, MA. Address for correspondence and reprints: Christopher Kabrhel, MD, Harvard Affiliated Emergency Medicine Residency, Brigham and Women’s Hospital/Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114. Fax: 617-724-0917; e-mail: ckabrhel@partners.org.

Copyright Hanley & Belfus, Inc. Jul 2003