Pityriasis lichenoides
What is it?
Pityriasis lichenoides is an uncommon cutaneous rash of uncertain aetiology. The acute form, pityriasis lichenoides et varioliformis acuta (PLEVA), and the chronic form, pityriasis lichenoides chronica (PLC), sit at either end of a disease spectrum with many patients showing overlapping features.
The eponym Mucha–Habermann disease is sometimes applied to the entire spectrum of PL but is often reserved for the particularly severe ulcero-necrotic variant of PLEVA.
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Signs & symptoms
PLEVA presents abruptly with a rapidly progressive rash:
* 10-50 reddish brown, erythematous, ovoid papules, 5-15mm in diameter
* Mainly on the trunk and proximal extremities
* Evolution into vesicles, pustules, haemorrhagic crusts, and ulcers
* Pruritus or burning sensation
* Most cutaneous lesions heal with transient or persistent hyper- or hypo-pigmentation.
* Constitutional symptoms are usually mild (see complications below).
PLC presents more slowly over several days with:
* Larger numbers of small erythematous papules with a brown hue visible on diascopy
* Mica-like scale on more established lesions
* Lesions at various stages of evolution
* Patients often experience periods of relapse and exacerbation.
Patients often show features of both PLEVA and PLC, and PLEVA may evolve into PLC. Mucosal lesions have been reported.
Diagnosis
The diagnosis can often be made on clinical grounds but is usually confirmed with a skin biopsy, which helps to exclude other important differential diagnoses.
Histological features of PLEVA include:
Other tests, such as screening for viral, bacterial, and toxoplasma infection may be considered, depending on the severity of the presentation.
Treatment
It is important to recognise that there have been no randomised controlled trials regarding treatment, and the natural history of pityriasis lichenoides makes interpretation of anecdotal reports difficult.
* PLEVA is most commonly treated with prolonged courses of erythromycin (in young children) or doxycycline. They are used for their anti-inflammatory effects rather than their antibacterial properties.
* Topical corticosteroids are of little value.
* Antihistamines may reduce itch.
* Phototherapy, usually narrow band UVB, is often the preferred treatment for pityriasis lichenoides chronica.
* Methotrexate and other immunosuppressive agents may be considered for refractory or very severe cases.
☝️ This is not a substitute for professional medical advice. Please consult with your physician before making any medical decision.
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