Investigation, diagnosis

• extraction of mite from the burrow using a sharp needle
• ink test - to show a burrow
• microscopic examination of skin scrapings (1)
  • skin scrapings are taken with a blunt scalpel blade or sterile needle point. If mites, faecal pellets, eggs or eggshells are seen it confirms the diagnosis of scabies (but it is not necessary to make a diagnosis) (1)
  • when direct examination is not possible or in atypical cases a skin biopsy may be done to confirm the diagnosis (1)

Note that scabies should not be excluded when a history of itching is lacking (1):

• some people do not seem to suffer from itch
• some are reluctant to admit possible scabies diagnosis
• very young babies may not scratch, they might feed poorly and seem miserable

Classical scabies should be differentiated from (1):

• animal scabies occasionally infesting humans, which is usually spread from pets. The distribution of the lesions are in areas that have been in contact with pets
• pubic and body lice, insect bites
• dermatological conditions such as Acropustulosis, which is a recurrent self-limited, pruritic, vesiculopustular eruption of the palms and soles, occurring in infants aged 2-3 years, atopic eczema, bullous pemphigoid, contact dermatitis, dermatitis herpetiformis, folliculitis, Grover's disease, Impetigo, Langerhan's cell histiocytosis, lichen planus, neurodermatitis, prurigo nodularis, seborrhoeic dermatitis, SLE and urticaria pigmentosa

Reference:

• 1. Engelman D, Yoshizumi J, Hay RJ, et al. The 2020 International Alliance for the Control of Scabies Consensus Criteria for the Diagnosis of Scabies. Br J Dermatol. 2020 Nov;183(5):808-820.