Pityriasis lichenoides is an umbrella term for a spectrum of rare benign skin disorders thought to be T-cell mediated in response to an environmental antigen that is most likely viral.
There are three types, listed here in descending order of frequency:
- Pityriasis lichenoides chronica (PLC): an almost asymptomatic outbreak of papules resembling pityriasis rosea that presents over weeks or months, often lapsing and recurring over a long period of time.
Image from the Dermatology Atlas
- Pityriasis lichenoides et varioliformis acuta (PLEVA): an acute outbreak of itchy or sore papules with crusts that can be mistaken for guttate psoriasis, a vasculitis, or, in the early stages, chickenpox.
Image from the Dermatology Atlas
- Febrile ulceronecrotic PLEVA: a severe, rare form of PLEVA with constitutional symptoms like fever and which is a dermatological emergency much like Stevens-Johnson syndrome. Also known as febrile ulceronecrotic Mucha-Habermann disease. Fewer than 100 cases have been reported in the literature.
- The exact frequency of the three types of pityriasis lichenoides is not known because it is often not formally diagnosed; however, it is likely to be rare.
- In adults it tends to come on in the 20s or 30s, with a slight male predominance.
- It can occur in children, however, with an average age of onset of 6 years.
- The cause of pityriasis lichenoides is not yet known but two major theories exist:
- A hypersensitivity reaction to an infectious agent such as parvovirus.
- A relatively benign form of a T-cell lymphoproliferative disorder.
- Despite resembling a vasculitis, the histology does not show features of vasculitis such as fibrin or thrombi in the walls or lumen of vessels.
- Infections that have been associated with both PLC and PLEVA include Toxoplasma gondii, Epstein-Barr virus, HIV, cytomegalovirus, parvovirus, Staphylococcus aureus and group A beta-haemolytic streptococcus.
Pityriasis lichenoides chronica (PLC)
- PLC usually presents with small pink papules that turn a reddish-brown colour. It resembles pityriasis rosea.
- The eruption is often polymorphic, with lesions at different stages of development.
- PLC is usually distributed over the trunk, buttocks and proximal arms or legs. It may occur elsewhere but usually spares the face and the palms of the hands, unlike chickenpox.
- The lesions are covered with a firm shiny scale ('frosted glass') which can be peeled off to reveal a red-brown colour underneath.
- The lesions usually flatten out over a period of weeks or months.
Pityriasis lichenoides et varioliformis acuta (PLEVA)
- This subtype of pityriasis lichenoides presents acutely with numerous red papulo-vesicles that are itchy and sometimes painful. The lesions have ulcerated, necrotic or haemorrhagic features and in the early stages can resemble chickenpox.
- Unlike chickenpox the lesions of PLEVA do not involve the mucous membranes and they last considerably longer.
Febrile ulceronecrotic PLEVA (Mucha-Habermann disease)
- This very rare condition presents with necrotic ulcerations that coalesce rapidly, with a high fever and systemic upset. It is considered a dermatological emergency.
- Diagnosis is usually based on the history and clinical picture. If diagnostic doubt exists, skin biopsy may be necessary.
- Other investigations are directed towards possible associated diseases and the differential diagnosis; they may include antistreptolysin O titres, ESR, HIV screening, infectious mononucleosis tests, cytomegalovirus serology, Epstein-Barr virus serology and toxoplasma serology.
- Guttate psoriasis
- Pityriasis rosea
- Lichen planus
- Insect bites
- Dermatitis herpetiformis
- Secondary syphilis
For the relatively quiescent, asymptomatic condition of PLC, often no treatment is required. If the patient requests treatment, or would like to try to expedite resolution of the lesions, the following first-line therapies are described in the literature:
- Topical steroids to reduce irritation.
- Topical immunomodulators - eg, tacrolimus or pimecrolimus.
- Oral antibiotics; the most common being erythromycin and tetracycline, with an 80% response rate to three months of erythromycin.
Second-line therapies for either PLC or PLEVA include:
- Monotherapy using narrow-band UVB (NB-UVB). This has been shown to achieve a 90% complete response rate over eight weeks, obviating the need for systemic therapies.
- For resistant cases, systemic steroids, methotrexate, acitretin, dapsone or ciclosporin may be used.
For the much more serious condition of febrile ulceronecrotic PLEVA:
- Aggressive treatment with immunosuppressant and/or immunomodulating agents as well as intensive supportive care are recommended for febrile ulceronecrotic PLEVA.
- TNF-alpha inhibitors (eg, infliximab) may be useful for patients with febrile ulceronecrotic PLEVA, particularly in resistant cases.
- Treatment is likely to take place on a burns intensive care unit.
- With the right treatment almost all children will have full resolution at three monthsbut in total median time to resolution is reported as 21 months for children.
- In adults, for both PLC and PLEVA, prognosis is usually good. Resolution takes a few months for most patients, and a few years in others, with a median time to cure of eight months.
- Two thirds affected by a first outbreak, even if reaching full resolution, will have a relapse.
- Ulceronecrotic PLEVA carries a high morbidity and is potentially fatalbut with expert treatment it has been reported to be responsive to prednisolone, NB-UVB light therapy or methotrexate.
- For chronic lesions that seem resistant to standard therapy, there is the risk of transformation to a cutaneous T-cell lymphoma such as mycosis fungoides. Even if this has occurred histologically it does not necessarily mean they will progress.
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