Scabies, including crusted scabies

scabies · crusted scabies · Norwegian scabies · the itch · mites

Relentless itch, worse at night, in more than one member of the household - treat the contacts or it comes straight back.

GPBand C

Red flags

Crusted scabies - highly contagious, a common source of outbreaks, needing specialist advice, isolation precautions and combined oral and topical treatment
Two or more linked cases in one setting - UKHSA asks for health protection team contact where two or more people at a setting have scabies and are linked, for example by being in the same class, group or location. This is not confined to care homes, and a nursery with two cases qualifies
Secondary bacterial infection, particularly group A streptococcal, which can lead to post-streptococcal complications
Failure of treatment after correctly applied therapy and simultaneous contact treatment - reconsider the diagnosis or resistance
Scabies in a baby under 2 months - rare at this age, and permethrin 5% cream is licensed only from 2 months, so CKS says seek specialist advice before treating, for example from a paediatric dermatologist. In infants the distribution also includes the palms, soles, scalp and face

Recognise

On light skin

Small red excoriated papules with fine grey burrows a few millimetres long in the finger webs and on the wrists, and inflamed nodules on the genitals or axillae.

On brown and black skin

Burrows are difficult to see against brown and black skin, and the secondary papules appear as skin-coloured, darker or violaceous rather than red, so scabies is frequently missed or misdiagnosed as eczema. Rely on the history and the distribution, which are tone-independent: severe itch that is worse at night, and other affected household members. Examine the finger webs and wrists in good light, stretch the skin to bring burrows into relief, and consider dermoscopy if available. Scabies in darker skin more often produces prominent nodular lesions and marked post-inflammatory hyperpigmentation that persists long after successful treatment - which is a common reason for repeated, unnecessary re-treatment.

In any skin tone

Itch that is worse at night and disturbs sleep - the defining symptom
Other people in the household itching - ask directly, because this is often the strongest evidence
Burrows in the finger webs and on the wrists
Sparing of the head and neck in adults, but not in infants or the elderly
Itch persists for two to four weeks after successful treatment and is not treatment failure
Crusted scabies: thick, widespread, scaly crusted plaques, often with surprisingly little itch, in the elderly, immunosuppressed or institutionalised - carrying an enormous mite burden and extremely infectious

Distribution

Finger webs, wrists, elbows, axillae, around the nipples, umbilicus, buttocks and genitals. In infants and the elderly it also affects the palms, soles, scalp and face, which it spares in other adults.

Photographs

Scabies on the back of the hand and in the finger webs. The lesions are small pale or skin-coloured papules - against brown skin they read a — Scabies on the back of the hand and in the finger webs. **The lesions are small pale or skin-coloured papules** - against brown skin they read as lighter, not redder, than the surrounding skin. Side lighting and the finger webs are what find them. An itchy child with normal looking skin at arm's length may have this at 20 cm.
Fitzpatrick IV-VI (Fitzpatrick type estimated from the photograph, not stated by the source) · Oladokun RE, Lehloenya RJ, Hlela C, Ubesie AC, Katibi SO, Malande OO, Eley BS · Atlas of Paediatric HIV Infection, UCT Libraries Press 2018 - Chapter 4: Skin Infestations, p77 · CC BY 4.0

Infantile scabies on the palms and soles, which is a distribution seen in babies and not in older children or adults. On the pale palmoplant — Infantile scabies on the **palms and soles**, which is a distribution seen in babies and not in older children or adults. On the pale palmoplantar skin the lesions are visible as pink papules even though the same child's trunk may show nothing obvious. **Always undress a baby's feet and hands** - and remember that in infants the scalp and face are involved too, so treatment must include them.
Fitzpatrick IV-VI (Fitzpatrick type estimated from the photograph, not stated by the source) · Oladokun RE, Lehloenya RJ, Hlela C, Ubesie AC, Katibi SO, Malande OO, Eley BS · Atlas of Paediatric HIV Infection, UCT Libraries Press 2018 - Chapter 4: Skin Infestations, p77 · CC BY 4.0

Provenance for every photograph in this library: image licences. How much of the corpus still has no darker-skin photograph: skin tone coverage.

Mimics

Atopic eczema and infected eczema — The usual misdiagnosis. Eczema does not spare the head in a pattern like this, and does not make the whole household itch
Acute urticaria — Itchy but weals are transient and migratory; scabies lesions are fixed
Impetigo — Secondary infection of excoriated scabies is common and both need treating
Head lice — Another infestation to ask about in a household with itch, though the distribution is entirely different
Pompholyx — Both itch intensely and both involve the finger webs, but scabies has burrows, affects contacts and is worst at night

What to do in the ED

Treat with topical permethrin 5% per the BNF and local policy, applied over the whole body including the face, neck, scalp and ears - in every patient, adult and child. The BNF is explicit that although the manufacturer recommends excluding the head and neck, application should be extended to the scalp, neck, face and ears. Leaving the head untreated is a recognised cause of apparent treatment failure. Larger patients may need up to two 30 g packs
Treat every household member, every close personal contact and every sexual partner from the past month at the same time, whether or not they itch. Not doing this is the commonest cause of apparent treatment failure - and a partner outside the household is neither a household member nor an obvious 'close contact' to a hurried reader. CKS notes that referral to genito-urinary medicine may be needed for partner notification
Explain the application properly: cool dry skin, under the nails, left on for the specified duration, repeated after a week
Warn explicitly that itch continues for two to four weeks after successful treatment - otherwise the patient re-attends or re-treats unnecessarily
Wash clothing, bedding and towels at a hot wash on the day of treatment
Treat secondary bacterial infection where present
Give UKHSA's setting advice, because it is what the parent or employer will ask about. A child of 5 or under, or any child who cannot follow the contact advice, stays away from nursery or school until 24 hours after completing their first treatment. Older children and young people attend as usual but must avoid close skin contact until the first treatment is complete. Close contacts, including household members, are treated but do not need to stay away
For crusted scabies, or any institutional outbreak, seek specialist and health protection advice rather than managing it as an individual case

Disposition

Treat and discharge with contact treatment arranged. Specialist and health protection involvement for crusted scabies or an institutional outbreak.

Safety-netting

Everyone in the house must be treated on the same day, even if they have no itch at all - this is the main reason scabies comes back. The itch will carry on for up to four weeks after successful treatment; that does not mean it has failed. Seek advice about re-treating if the itch is still there beyond two to four weeks after the last application, or if new burrows appear after treatment - CKS gives both as reasons to re-treat. Return if the skin becomes hot, painful, weeping or crusted with a fever, or if the itch is no better after four weeks.

Local variation

CKS treats permethrin 5% cream and oral ivermectin as two licensed regimens of similar effectiveness for uncomplicated classical scabies in anyone aged 2 months and over - ivermectin 200 micrograms/kg as a single dose, repeated after a further 7 days - and says to consider ivermectin over permethrin where there is pre-existing eczema or another skin condition that may lead to hypersensitivity. Crusted disease may need both together. UK availability and prescribing routes still vary, so know what yours allows rather than assuming ivermectin is unavailable.

Sources

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