Pityriasis Lichenoides Chronica

Pityriasis lichenoides chronica is a chronic papulosquamous eruption of small, red brown, scaly papules that arise in crops and heal with pigment change. It is the milder end of a spectrum with pityriasis lichenoides et varioliformis acuta.

It affects children and young adults, with a slight male predominance, and has a prolonged, relapsing course that often lasts months to years. It usually resolves spontaneously, and most cases settle within a few years.

The cause is unknown. Proposed triggers are infections (Epstein-Barr virus, parvovirus B19, Toxoplasma gondii) and drugs, and some cases show clonal T-cell populations without progression to lymphoma in most patients.

Pathophysiology.

The disease is a T-cell mediated lymphocytic inflammatory reaction, with a predominance of CD8 positive cells, that targets the dermal vessels and the epidermis. This causes interface change, extravasation of red cells and parakeratosis.

• Crops of 3 to 10 mm red brown papules with an adherent mica like scale that peels off as one piece.
• Distribution on the trunk, proximal limbs and flexures, with sparing of the face, palms and soles.
• Lesions at different stages of evolution, resolving over weeks to leave hypopigmented or hyperpigmented macules. Scarring is uncommon.
• Mild or no itch, with no systemic upset.

Red flags.

• Persistent plaques or lesions that fail to resolve, with atypical scale, raising concern for mycosis fungoides.
• Ulceration, necrosis or fever, suggesting the acute form.
• Lymphadenopathy.

• Clinical, supported by dermoscopy and biopsy when the diagnosis is uncertain.
• Skin biopsy: parakeratosis, mild interface change, a superficial perivascular lymphocytic infiltrate and extravasated red cells.
• Syphilis serology to exclude secondary syphilis, and HIV testing when risk factors are present.
• T-cell receptor gene studies and immunophenotyping for atypical or persistent lesions.

Differential diagnosis. Guttate psoriasis, pityriasis rosea, lichen planus, secondary syphilis, drug eruption, viral exanthem, early mycosis fungoides, lymphomatoid papulosis and insect bites.

• Reassure. The disease is benign, and spontaneous resolution is usual, though relapses occur.
• Emollients, and moderate potency topical corticosteroid (clobetasone butyrate 0.05%) or potent corticosteroid (betamethasone valerate 0.1%) once daily for 2 to 4 weeks for itch or inflamed lesions.
• Narrowband ultraviolet B two to three times weekly for 8 to 12 weeks is the most effective option for extensive or persistent disease.
• Oral antibiotics have weak evidence of benefit: 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 for 6 to 12 weeks in people over 12 years.
• Resistant disease: methotrexate 7.5 to 15 mg once weekly (maximum 25 mg) with folic acid 5 mg weekly.

Monitoring. Review every 3 months. Re-biopsy if lesions change or fail to resolve within 2 to 3 years.

Referral and escalation. Refer to dermatology for atypical features, persistence, or suspected lymphoma.

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