History

Fact Explanation
Pruritus : Characteristically at night or after a hot bath [1] Immune response to mites and its excreta [1]
Rash : Papules/ Nodules/ Vesicles/ Eczematous [1] Immune response to mites and its excreta [1]
Sites of lesions : Interdigital spaces and the flexor surfaces of the wrist, axillae, waist, feet, ankles. In females the skin surrounding the nipple, In males the scrotum and penis is involved [1] Commonest sites for scabies mite for burrowing
Contact history of Scabies infection : Family members/ Institutional setting [2] The commonest route of transmission is direct skin-to-skin contact [2]
Fever [3] Following secondary bacterial infection [3]
References
  1. Leone PA. Scabies and Pediculosis Pubis: An Update of Treatment Regimens and General Review. Clinical Infectious Diseases. (2007) 44 (Supplement 3): S153-S159. doi: 10.1086/511428
  2. Chosidow O. Scabies. The New England Journal of Medicine. 2006; 354:1718-1727April 20, 2006. DOI: 10.1056/NEJMcp052784
  3. Walton SF, Currie BJ. Problems in Diagnosing Scabies, a Global Disease in Human and Animal Populations. Clinical Microbiology Reviews. April 2007; 20(2) : 268 -279

Examination

Fact Explanation
Rash: Papules/ Nodules/ vesicles/ Pustules often accompanied by eczematous lesions. Symmetrically distributed. Sites : on the volar wrists, between the fingers, on the elbows, and on the penis, In skin folds under the breasts and around the navel, axillae, belt line, buttocks, upper thighs, and scrotum [1] sensitization reaction against the excreta of the mite present in the burrows [1]
In Infants: In addition to the above sites the face, scalp, neck, palms, and soles are also involved [1] sensitization reaction against the excreta of the mite present in the burrows [1]
Burrows - They are seen by appear as dark wavy lines and measure up to 5 mm. Commonest locations are on the volar wrists, between the fingers, on the elbows, and on the penis [1] The scabies mite makes the burrow by digesting and consuming the horny layer of the epidermis [2]
Secondary infection of lesions [2] Due secondary bacterial infections [2]
Crusted Scabies - Presents as a psoriasiform dermatitis with a peripheral distribution. Erythematous scaly eruption involving the face, neck, scalp, and trunk [3] Due to hyperinfestation with thousands of mites [3]
References
  1. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison's Principles of Internal Medicine. 18th edition. New York. McGrawHill-Medical.
  2. Walton SF, Currie BJ. Problems in Diagnosing Scabies, a Global Disease in Human and Animal Populations. Clinical Microbiology Reviews. April 2007; 20(2) : 268 -279
  3. Huang YC, Chen MJ, Shih PY. Crusted Scabies on the Scalp Mimicking Seborrheic Dermatitis. Clinical Infectious Diseases. (2012) 54 (6): 882. doi: 10.1093/cid/cir890

Differential Diagnoses

Fact Explanation
Atopic dermatitis [1] Patients may have other symptoms of atopy such as hay fever, Asthma
Urticaria [1] Patient may history of allergy, recurrent attacks of urticarial rash
Varicella [2] Vesicles on erythematous papules. Vesicles gradually become pustules and heal by crusting. Lesions occur in crops. Initially centrally on the trunk.
Insect bite - eg; Bed bug [3] More prominent erythematous papules seen with bed bugs and other arthropod bites. Bed bugs tend to attack easily accessible, exposed areas [3]
Tinea infection [4] However Central resolution and erythematous edge will be present. Lesions often Annular.
References
  1. Dodd WA. Itching skin in children. British Columbia Medical Journal, Vol. 46, No. 10, December 2004, page(s) 510-515
  2. ELY JW, STONE MS. The Generalized Rash: Part I. Differential Diagnosis. American Family Physician. 2010 Mar 15;81(6):726-734.
  3. Huntington MK. When bed bugs bite. Journal of Family Practice. 2012 July;61(07):384-388
  4. Walton SF, Currie BJ. Problems in Diagnosing Scabies, a Global Disease in Human and Animal Populations. Clinical Microbiology Reviews. April 2007; 20(2) : 268 -279

Investigations - for Diagnosis

Fact Explanation
Demonstration of Mite/ Eggs/ Fecal pellets from Burrows [1] Sarcoptes scabei mite/ eggs/ Fecal pellets
Biopsies, scrapings of papulovesicular lesions, and microscopic inspection of clear adhesive tape lifted from lesions [1] Demonstration of Mite/ Eggs/ Fecal pellets
References
  1. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison's Principles of Internal Medicine. 18th edition. New York. McGrawHill-Medical.

Investigations - Fitness for Management

Fact Explanation
Renal function tests [1] Secondary infection of skin lesions by group A β-hemolytic streptococci may increase the risk of the child developing Glomerulonephritis
References
  1. Leone PA. Scabies and Pediculosis Pubis: An Update of Treatment Regimens and General Review. Clinical Infectious Diseases. (2007) 44 (Supplement 3): S153-S159. doi: 10.1086/511428

Investigations - Followup

Fact Explanation
Repeat of Biopsies, scrapings of papulovesicular lesions, and microscopic inspection of clear adhesive tape lifted from lesions one month after treatment [1] Evidence of cure requires follow up for almost one month. As this allows time for lesions to heal and for any eggs and mites to reach maturity in case of treatment failure [2]
References
  1. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison's Principles of Internal Medicine. 18th edition. New York. McGrawHill-Medical.
  2. Strong M, Johnstone P. Interventions for treating scabies (Review). The Cochrane Library 2010, Issue 10. Wiley publishers.

Investigations - Screening/Staging

Fact Explanation
Skin biopsy for Histology Demonstration of nonspecific, delayed hypersensitivity reaction
References
  1. Chosidow O. Scabies. The New England Journal of Medicine. 2006; 354:1718-1727April 20, 2006. DOI: 10.1056/NEJMcp052784

Management - General Measures

Fact Explanation
All bedding, towels, and clothing should be washed in warm water. [1] To eradicate Scabies mite
Patients should be instructed to avoid contact with their sex partner until they have been treated and both individuals have been seen in follow-up [1] The commonest route of transmission is direct skin-to-skin contact [2]
Anithistamines - To reduce pruritus [2] antihistamines reduces histamine release associated with the Immune response to scabies mites and its excreta
Antibiotics oral/ Topical - According to Antibiotic sensitivity test [3] Due secondary bacterial infections [4]
References
  1. Leone PA. Scabies and Pediculosis Pubis: An Update of Treatment Regimens and General Review. Clinical Infectious Diseases. (2007) 44 (Supplement 3): S153-S159. doi: 10.1086/511428
  2. Dodd WA. Itching skin in children. British Columbia Medical Journal, Vol. 46, No. 10, December 2004, page(s) 510-515
  3. Walton SF, Currie BJ. Problems in Diagnosing Scabies, a Global Disease in Human and Animal Populations. Clinical Microbiology Reviews. April 2007; 20(2) : 268 -279
  4. Abdallah M, Zaki SMI, El-Sayed A, Erfan D. Evaluation of secondary bacterial infection of skin diseases in Egyptian in- & outpatients & their Sensitivity to antimicrobials. Egyptian Dermatology Online Journal. Vol. 3 No 2:3, December 2007.

Management - Specific Treatments

Fact Explanation
Permethrin 5% - Topical. Applied overnight once a week for two weeks to the entire body, including the head in infants. For a contact period of eight hours. [1] Effective scabicide. Low side effects, can be used safely in children. Treat all household contacts. [1], [2]
Benzyl benzoate - 10% / 25%. : Should be applied below the neck three times within 24 hours without an intervening bath [1] Effective scabicide. Neurotoxic to mites. Contraindicated in pregnancy, lactation, infants, and children less than 2 years of age [1]
Ivermectin - Oral anti scabies drug [1] Neurotoxic to scabies mite. Relatively safe. however contraindicated in patients' with CNS disease, pregnancy, lactation, and in children less than 5 years of age. [1]
Lindane lotion - 1% {1} No longer recommended due to CNS toxicity [2]
Malathion [1] Kills the mite due to organophosphate insecticide that irreversibly blocks the enzyme acetylcholinesterase. It is not recommended for humans now due to side effect profile [1]
References
  1. Karthikeyan K. Treatment of scabies: newer perspectives. Postgraduate Medical Journal 2005;81:7-11. BMJ. doi:10.1136/pgmj.2003.018390
  2. Leone PA. Scabies and Pediculosis Pubis: An Update of Treatment Regimens and General Review. Clinical Infectious Diseases. (2007) 44 (Supplement 3): S153-S159. doi: 10.1086/511428