Pityriasis Lichenoides

Pityriasis lichenoides is a rare skin disorder of unknown aetiology characterized by multiple papules and plaques. There are two types:

• An acute, short-lived form usually found in children (pityriasis lichenoides et varioliformis acuta; PLEVA)
• A more chronic form known as pityriasis lichenoides chronica; PLC

• In approximately 44,000 patients seen over 10 years in 3 catchment areas in Great Britain, 17 cases of PLEVA were diagnosed.¹
• Usually presents before the age of 30 years.
• There appears to be an association with certain infections in some patients, e.g. Epstein-Barr virus, Toxoplasma gondii, and HIV infection.
• However the majority of cases are idiopathic and cannot be associated with any particular cause.

• Pityriasis lichenoides et varioliformis acuta (PLEVA) and PLC are not distinct diseases. They are different presentations of the same process, with the process being more rapidly accelerated in PLEVA.
• PLEVA lesions may evolve into lesions of PLC. Lesions that are clinically consistent with both PLEVA and PLC are often found on physical examination. In both PLEVA and PLC, lesions are scattered but discrete.
• Most lesions heal with post-inflammatory changes, e.g. transient or persistent hyperpigmentation.
• Dark-skinned people rarely may present with widespread macular hypopigmentation. This variant is most common in children.
• Lesions may be symmetrical or asymmetrical, and particularly occur on the trunk, buttocks, and proximal extremities. Lesions may also appear on the palms, soles, face and scalp.

Pityriasis lichenoides et varioliformis acuta (PLEVA)

• The common variant of PLEVA presents with the sudden appearance of multiple papules on the trunk, buttocks, and proximal extremities. Papules rapidly progress to vesicles and haemorrhagic crusts.
• Minor systemic upset may occur.
• Lesions of PLEVA may be associated with burning and pruritus.
• The spots come up in crops. The rash may resemble chickenpox but takes much longer to clear.
• Ulceronecrotic PLEVA presents with a sudden eruption of diffuse coalescent necrotic ulcerations associated with high fever, malaise and myalgia.

Pityriasis lichenoides chronica (PLC)

• PLC presents as small erythematous-reddish brown papules, with more lesions compared to PLEVA.
• A fine scale is usually seen. The eruption is often polymorphic, with lesions at different stages of development.
• PLC usually develop subacutely, over days. It is also distributed over the trunk, buttocks, and proximal extremities.
• The spots look less angry and are covered with a firm shiny scale. The scale, covering the top of a spot, can be scraped off as a single chunk, to reveal a shiny brownish surface underneath.
• The spots fade within three to four weeks but new spots may then appear.
• The rash can clear up in a few weeks or persist for years.

Diagnosis is based on clinical appearance and usually confirmed by skin biopsy (shows a lymphocytic vasculitis).

• Guttate psoriasis
• Tinea corporis
• Pityriasis rosea
• Lichen planus
• Chickenpox
• Insect bites
• Dermatitis herpetiformis
• Secondary syphilis: patient unwell and with lymphadenopathy

• Often no treatment is required and the condition resolves spontaneously. In cases where treatment is necessary, recommended first-line therapies include:
• Sun exposure may help to resolve lesions but sunburn should be avoided.
• Topical steroids to reduce irritation.
• Topical immunomodulators, e.g. tacrolimus or pimecrolimus.
• Oral antibiotics: the most common antibiotics used are erythromycin and tetracycline.
• Phototherapy is beneficial in the treatment of subacute or chronic disease (sun exposure in summer helps). Both psoralen plus UV-A (PUVA) and UV-B may result in clearing but relapses are not uncommon.
• Other treatments occasionally required for severe, resistant PLC and PLEVA include methotrexate, acitretin, dapsone, ciclosporin.

• Usually good, with spontaneous resolution. Resolution may just take several months but may take much longer.
• Ulceronecrotic PLEVA can lead to scarring.