Scabies (and crusted scabies)

Latest update 11/12/10

This chapter is set out as follows:

• Introduction
• Key diagnostic features
• Crusted scabies (syn. Norwegian scabies)
• Management

Introduction

• Human scabies is caused by infection with a mite known as Sarcoptes scabiei var. hominis
• Scabies is normally acquired by skin-to-skin contact with someone else who has scabies. It is frequently acquired from children but it can occasionally be sexually transmitted, or acquired via bedding and furnishing as the mite can survive for a few days away from its human host

Key diagnostic features

• Symptoms
  • Itch, which is characteristically worse at night
• Distribution
  • The trunk and limbs are the predominant sites that are affected
  • The face and scalp are rarely involved other than in infants and bed-bound elderly patients
• Morphology
  • A generalised rash with erythema, papular and urticated lesions. This is caused by an allergy to the mites and their products, and may take several weeks to develop after infestation
  • Burrows – are seen as very small irregular tracks. These are most common on the sides of fingers, the webs, the borders of the hands, the wrists and the feet. They can also be found on the male genitalia, axillae and buttocks
  • Nodules – most commonly seen in the axillae, groin and on the shaft of the penis. May persist for several weeks after the scabies has been eradicated
  • Papules and pustules on the palms and soles are characteristic of scabies in infancy
• Dermoscopy – 'jet-plane' appearance
• Secondary infection – with impetigo is relatively common. Patients develop local areas of pustules / crusting  
  
• Scabies should be part of the differential diagnosis of an itchy rash where there is no personal or FHx of eczema or other atopic disorders, especially if no other cause can be readily identified. It is possible for patients with eczema to also acquire scabies

Crusted scabies (syn. Norwegian scabies)

• Uncommon
• Highly contagious with huge numbers of mites
• Most commonly arises in patients with the following:
  • Neurological impairment or dementia
  • Downs syndrome
  • Immunosuppression
  • Who have been inappropriatley treated with potent or super-potent topical steroids
• Clinical features - generalised scaly rash. The itch is often significantly less than with classical scabies. The scalp may be involved
• Public health must be informed if it occurs in an institution such a nursing home 

Management

• Provide a patient information leaflet
• 5% permethrin cream (Lyclear ®) is the treatment of choice; other scabicides are more irritant and less effective. 1 x 30 g tube should cover an average adult
• Treat as follows:
  • The cream should be applied uniformly over all the body from the neck downwards. Pay special attention to skin creases, genital area and underneath the nails. The face and scalp should only be treated if they are affected, which is uncommon in adults and older children (Lyclear cream rinse should be used for the scalp)
  • Wash off after 8-24 hours (note the cream should be re-applied to the hands if they are washed within 8 hours of first applying the cream)
  • Thereafter, launder all bed linen, towels and clothing
  • Repeat treatment after seven days
• Treat secondary infection if present with a systemic antibiotic e.g. flucloxacillin or erythromycin if allergy to penicillin
• Contacts – include anyone living in the same house, partners and others who have significant contact though child care e.g. in some situations grandparents. Remember other contacts can be infected with scabies but remain asymptomatic for several weeks. All such contacts need to be managed in exactly the same way as the patient, however for most only one treatment is needed. Only symptomatic contacts require two treatments
• Persistent rash or itch - the rash or itch of scabies may not clear for at least a month after successful treatment. Nodules can occasionally persist for several months. These are not contagious. Treat with mild/moderate topical steroids
• Re-infection is common if patients and contacts are not compliant: re-treat and check contacts
• Patients with severe scabies, or crusted scabies need frequent applications of permethrin, sometimes for several weeks. Oral ivermectin is sometimes used in such cases
• Discussion with / referral to a dermatologist should be considered for the following cases:
  • Failure to respond to adequate treatment of the patient and contacts
  • Diagnostic uncertainty
  • Crusted scabies

	Figure 1 – Scabies (copied with kind permission from Dermatoweb)
	Figure 2 – Scabies. Close up of a burrow
	Figure 3 – Dermoscopic appearance of the mite The brown triangle denotes the mites head with a 'jet-plane' appearance (black arrows)
	Figure 4 – Scabies with localised crusting This patients hands had become heavily infested due to treatment with topical steroids and the use of cotton gloves
	Figure 5 – Same patient as figure 4 Involvement of the wrists
	Figure 6 – as above. Note the burrow
	Figure 7 – Two sisters Same patient as figure 4. Her sister and other family members had also become infested
	Figure 8 -Scabies on the trunk with urticated papules
	Figure 9 – Scabetic nodules on an infant
	Figure 10 – Scabetic nodules on penis
	Figure 11 – Scabies. Sole of an infant
	Figure 12 – Scabies Close up of pustules on an infants sole
	Figure 13 – Scabies with facial involvement in an infant
	Figure 14 – Norwegian scabies