Pityriasis Lichenoides et Varioliformis Acuta

Pityriasis lichenoides et varioliformis acuta is an acute, self-limited eruption of crops of erythematous papules that evolve to vesicles, pustules and haemorrhagic, necrotic crusts. Lesions heal with varioliform (smallpox like) scars and pigment change.

It affects children and young adults, with a slight male predominance, and may follow infection. A severe febrile ulceronecrotic variant with large confluent necrotic ulcers and high fever is rare.

Proposed triggers are infections (Epstein-Barr virus, parvovirus B19, Toxoplasma gondii, HIV) and drugs, and the condition is regarded as a T-cell mediated vascular reaction. It runs a course of weeks to months, with spontaneous resolution in most cases.

Pathophysiology.

A cytotoxic T-cell reaction produces lymphocytic vasculitis with endothelial damage, keratinocyte necrosis and extravasation of red cells. The infiltrate is wedge shaped and dense, with CD8 positive cells predominating. Clonal T-cell receptor rearrangement is found in some cases.

• Crops of red papules on the trunk, flexures and proximal limbs that become vesicular, pustular and then ulcerated with haemorrhagic crusts.
• Lesions at different stages, healing with varioliform scars and hypopigmented or hyperpigmented macules.
• Mild itch or burning, malaise and low grade fever in some. Face, palms and soles are usually spared.
• Febrile ulceronecrotic form: sudden onset with high fever, large painful necrotic ulcers, lymphadenopathy and sometimes systemic involvement.

Red flags.

• High fever with extensive necrotic ulceration, suggesting the febrile ulceronecrotic variant.
• Secondary infection, sepsis or haemorrhage.
• Lesions with large atypical cells on biopsy, suggesting lymphomatoid papulosis.

• Clinical, with confirmation by skin biopsy: interface dermatitis with keratinocyte necrosis, a dense wedge shaped lymphocytic infiltrate, and red cell extravasation.
• Varicella zoster virus PCR, syphilis serology, HIV test and serology for Epstein-Barr virus when clinically appropriate.
• Full blood count, inflammatory markers and cultures in febrile disease.
• T-cell receptor gene studies and CD30 staining to exclude lymphomatoid papulosis and lymphoma.

Differential diagnosis. Varicella, lymphomatoid papulosis, leukocytoclastic vasculitis, arthropod bites, secondary syphilis, rickettsial infection, folliculitis, drug eruption and Langerhans cell histiocytosis.

• Mild to moderate disease: emollients, moderate to potent topical corticosteroid (betamethasone valerate 0.1%) once daily for 2 to 4 weeks, and narrowband ultraviolet B two to three times weekly.
• Oral antibiotics for 6 to 12 weeks have weak evidence: erythromycin 30 to 50 mg/kg/day in 2 to 4 divided doses in children (adults 500 mg twice daily to four times daily, maximum 4 g daily), or doxycycline 100 mg twice daily in people over 12 years.
• Resistant or extensive disease: methotrexate 7.5 to 15 mg once weekly (maximum 25 mg) with folic acid 5 mg weekly. Ciclosporin 2.5 to 5 mg/kg/day in two divided doses is an alternative.
• Febrile ulceronecrotic variant: admit, give analgesia, fluid and nutritional support, wound care and treatment of infection, with early methotrexate 10 to 25 mg once weekly, prednisolone 0.5 to 1 mg/kg/day, or ciclosporin.
• Sedating antihistamine such as chlorphenamine 4 mg at night for itch.

Monitoring. Review every 2 to 4 weeks until resolution. For methotrexate monitor full blood count, liver tests and renal function.

Referral and escalation. Refer to dermatology for diagnosis and biopsy, and urgently for the febrile ulceronecrotic variant.

Special groups. Avoid doxycycline under 12 years and in pregnancy. Methotrexate is contraindicated in pregnancy.