Pityriasis lichenoides, including PLEVA

PLEVA · pityriasis lichenoides et varioliformis acuta · PLC · pityriasis lichenoides chronica · Mucha-Habermann disease

Recurring crops of papules that crust, erode and scar over months - benign, frequently misdiagnosed as chickenpox or scabies, and a dermatology referral rather than an ED problem.

ROUTINE DERMBand B

Red flags

Febrile ulceronecrotic Mucha-Habermann disease - high fever with rapidly extending necrotic ulcers and systemic illness. It is rare and it is a genuine emergency; admit and involve dermatology urgently
Extensive ulceration with secondary infection

Recognise

On light skin

Pink to red-brown papules that develop a central scale, then a dark adherent crust, sometimes eroding to leave a varioliform scar. In the chronic form, smaller scaly papules with a mica-like scale that lifts off whole.

On brown and black skin

The erythema of the fresh papule is poorly visible, but this condition is unusually well suited to recognition in darker skin because its diagnostic features are structural rather than coloured - the central scale, the adherent dark crust, the erosion, the varioliform scar and the coexistence of several lesion ages are all tone-independent. The pigmentary aftermath is more prominent and more distressing than in pale skin: marked post-inflammatory hyperpigmentation, and in the chronic form hypopigmented macules that are conspicuous against brown and black skin and may persist long after the disease is inactive. That dyspigmentation is often the presenting complaint rather than the papules, and it reflects pigment lability rather than active disease - say so, because families frequently read it as the condition spreading. No skin-of-colour-specific series was identified for pityriasis lichenoides; this draws on general sources.

In any skin tone

Crops of lesions at different stages at the same time - the most useful single feature
A central adherent crust, and varioliform (pock-like) scars where lesions have healed
Months-long course with recurring crops, not a single self-limited eruption
The patient is systemically well
Acute (PLEVA) and chronic (PLC) forms occur with roughly equal frequency and frequently overlap in one patient

Distribution

Trunk, buttocks and proximal flexural limbs most heavily, in crops. Lesions of different ages coexist, which is the clue - fresh papules alongside crusted ones alongside scars. Mean age of onset in childhood series is 6.5 years with a slight male predominance.

Photographs

Pityriasis lichenoides et varioliformis acuta on the upper thigh. Look at the ages rather than the colour: papules of several different size — Pityriasis lichenoides et varioliformis acuta on the upper thigh. **Look at the ages rather than the colour**: papules of several different sizes and stages are present at once, some fresh and some already settling, which is the feature that separates this from a single-crop viral exanthem and the reason it is so often called recurrent chickenpox. This is light skin, which is a limitation of this page and not of the disease.
Fitzpatrick II (Fitzpatrick type estimated from the photograph, not stated by the source) · Florian Jesse (uploader; Commons records no machine-readable author) · Wikimedia Commons - PLEVA.jpg · Public domain

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

Mimics

Chickenpox (varicella) — The commonest misdiagnosis. Both show lesions at different stages simultaneously. Chickenpox resolves in two weeks and the child is unwell; pityriasis lichenoides recurs over months in a well child
Scabies, including crusted scabies — Also itchy papules with crusting; scabies has burrows, a nocturnal itch and affected contacts
Psoriasis, including guttate — Guttate psoriasis is also small scaly papules on the trunk after infection, but with silvery scale and no crusting, erosion or scarring
Pityriasis rosea — Also truncal and scaly, but with a herald patch, a collarette of scale and a single six-to-eight-week course
IgA vasculitis (Henoch-Schonlein purpura) — Both can look purpuric on the legs; IgA vasculitis is palpable purpura over days with joint, gut and renal features
Molluscum contagiosum — Also discrete papules in a well child, but umbilicated and pearly, without scale, crust or scarring

What to do in the ED

Recognise it and say what it is not - most of these children arrive labelled as recurrent chickenpox or as scabies that will not clear, and have been treated repeatedly for both
Examine for lesions of several different ages, and look for varioliform scars from earlier crops - that history is often visible on the skin even when the parents have not noticed it
Do not treat with permethrin or aciclovir on spec
Refer to dermatology. Diagnosis is usually clinical but biopsy is sometimes needed, and the treatment evidence base sits entirely outside the ED - a systematic review puts narrowband UVB first line and oral erythromycin second
Be straight that the course is months and that it comes in crops; the recurrence is the disease, not a treatment failure

Disposition

ROUTINE DERM

Routine dermatology referral. The course is benign in the great majority, but long-term follow-up is recommended because transformation to cutaneous T-cell lymphoma, while rare, has been reported - that is a reason for dermatology to hold the patient, not a reason to alarm the family in the ED.

Safety-netting

Return urgently for fever with rapidly spreading ulcers or necrotic areas, or if the patient becomes systemically unwell - that presentation is rare but serious. Otherwise expect new crops over months; that is the expected course and not a deterioration.

Local variation

Access to narrowband UVB phototherapy for children varies considerably between units, and in some regions it means travelling to a centre. Dermatology will know the local route; the ED should not promise one.

Sources

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