Scabies is a highly contagious pruritic ectoparasitic infestation of skin mite Sarcoptes scabiei var. hominis. (Chouela et al., 2002; Currie and McCarthy, 2010) The scabies mite, an arachnid of the genus Acarus, was first identified by Bonomo in the year 1687 AD. The adult female is larger and responsible for reproduction of new eggs. Copulation occurs in small burrows excavated by the females. The burrows are usually not confined to the stratum corneum but are inclined downwards into the epidermis. The life cycle of the mite is 14 to 21 days. (‘Rook’s Textbook of Dermatology’, 2016)
Typical clinical presentation: Scabies can present in three distinct forms; common scabies, crusted scabies also known as Norwegian scabies, and nodular scabies. Common scabies has the classical presentation of nocturnal pruritus along with positive history of contacts. In crusted scabies patients present with thick crusted lesions on hands and feet, nail dystrophy, and eruptions with erythematous scaling with mild or absent pruritus. They usually harbor few hundreds to millions of mites and occur most frequently in patients with immunocompromised status. It is difficult to treat and highly contagious. Nodular scabies presents as nodules in flexural areas and is an allergic immune response to the feces of the scabies mite. (Heukelbach and Feldmeier, 2002; Chosidow, 2006) Clinical presentation in nursing home residents and how it differs: In debilitated, immunocompromised, or institutionalized patients, scabies may present with some atypical features of absent pruritus, truncal papulosquamous dermatoses and absence to reporting symptoms because of dementia or vocal disabilities. Aging causes the loss of epidermal undulations and progressive flattening of the undersurface of the epidermis which enables the scabies mite to move at a faster rate and hence multiply at a faster rate causing quicker than anticipated spread of scabies in aging patients who are more likely to be institutionalized in nursing homes. The coexistence of cognitive or functional disability in the geriatric patients may impair the ability to scratch and thus prevent effective elimination of the mite and reporting of the disease to the facility staff. (Wilson, Philpott and Breer, 2001)
Diagnosis: Most of the scabies patients are diagnosed by clinical evaluation. Absolute confirmation can only be declared after visualizing live mite or burrows under the microscope. The presence of mites, eggs, fragments of egg shells or scybala confirms the diagnosis. Dermoscopy has been getting popular in recent years for diagnosing or detecting the mite without going through ink tests or actual microscopes. Under dermoscopy on 40x magnification a classical ‘jet‐with‐contrail’ can be seen, which is actually the mite. A skin biopsy may confirm the diagnosis of scabies if a mite or parts of mite come under the slice. Howver mostly nonspecific signs are usually seen e.g. papillary oedema, & superficial and deep perivascular inflammatory cell infiltrates with numerous eosinophils. It is ssential in cases of crusted scabies or scabies in health care settings to have a confirmation of scabies so rest of the inhabitants and contacts can be treated.(‘Rook’s Textbook of Dermatology’, 2016) It is however very difficult to distinguish active infestation, residual skin reaction and reinfestation from each other.
Treatment: First line treatment is classical scabies include 5% permethrin solutions and/or oral ivermectin (200 mcg/kg). Second line agents include benzyl benzoate (10 or 25%), topical sulfur (6 to 33%), lindane and crotamiton. Permethrin is usually well tolerated however skin irritation can be a side effect. Use of lindane has fallen out of favor due to risk for systemic toxicity (e.g., seizures, and death in elderly and children). (Workowski, Bolan and for and Prevention, 2015; Salavastru et al., 2017) Crusted scabies however is mostly treated with a combination of two medications usually topical permethrin along with oral ivermectin. Antihistamines are given for relief of pruritus and topical mild potency steroids are given for post scabies eczema. General environmental preventive measures include laundering or sequestering items that came in close contact with the patients for example clothing with prolonged contact (>10 minutes) with the infested individual and adequate cleaning of rooms inhabited by patients with crusted scabies. Ivermectin is thought to potentiate GABA activity and drugs, such as barbiturates, benzodiazepines and valproic acid, which also enhance GABA activity, may increase its toxicity and should be avoided. Nursing home patients are usually on these medications.
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