Pityriasis Lichenoides
On this page
Direct answer
Pityriasis lichenoides is an inflammatory papulosquamous disorder with an acute form, pityriasis lichenoides et varioliformis acuta or PLEVA, and a chronic form, pityriasis lichenoides chronica or PLC. PLEVA produces crops of papules that necrose into haemorrhagic crusts and heal with varioliform scars, whereas PLC produces brown-red scaly papules that persist for months to years. Narrowband UVB phototherapy treats both forms, with oral antibiotics added in selected cases.
What you must remember
- PLEVA: an acute eruption of erythematous papules that evolve into vesicles and papulonecrotic lesions with haemorrhagic crusts, usually in children and young adults.
- PLEVA healing: lesions settle over weeks to a few months and often leave varioliform, pock-like scars, and the disease can be extensive; a rare febrile ulceronecrotic form is severe.
- PLC: a chronic eruption of brown-red, scaly papules on the trunk and limbs that persist for months to years without necrosis.
- Histology: PLEVA shows epidermal necrosis with vascular damage and a perivascular lymphocytic infiltrate; PLC shows parakeratosis and interface change, and the features overlap.
- Lymphoma caution: persistent, atypical or unresponsive lesions need biopsy, because lymphomatoid papulosis and cutaneous lymphoma can mimic the disease.
- Treatment: narrowband UVB for both forms, oral erythromycin or tetracycline for selected cases, topical steroids for PLC, and methotrexate for extensive PLEVA.
- Antibiotic caution: tetracyclines are avoided in young children because of tooth discolouration.
PLEVA against PLC
The two forms are distinguished more by course and lesion type than by site, and the table sets out the differences that exam stems usually test.
| Feature | PLEVA | PLC |
|---|---|---|
| Course | Acute, weeks to a few months | Chronic, months to years |
| Lesions | Papules that necrose into haemorrhagic crusts | Brown-red scaly papules without necrosis |
| Healing | Varioliform scars | Residual pigmentary change |
| Histology | Epidermal necrosis with vasculitic change | Parakeratosis and interface change |
| Usual treatment | Narrowband UVB, oral antibiotics, methotrexate if extensive | Narrowband UVB, topical steroids, oral antibiotics |
Necrotic, crusted papules that heal with varioliform scars point to PLEVA, while long-lasting scaly papules without necrosis suggest PLC. Persistent or atypical lesions in either form warrant biopsy, because lymphoma can mimic the picture.
Clinical history matters: an abrupt crop of necrotic papules in a child points to PLEVA, while a slowly evolving scaly eruption present for months points to PLC. Recording the number of lesions, the presence of crusts and the healing pattern at each visit helps track the response to phototherapy and antibiotics.
Where the exam tries to catch you
Pityriasis lichenoides questions test the acute and chronic distinction, the lymphoma caution and the choice of phototherapy.
- Trap: treating PLEVA as a benign rash that will clear untreated Correct: PLEVA can be extensive and scar, so phototherapy or antibiotics are often used.
- Trap: calling PLC psoriasis or pityriasis rosea Correct: PLC has brown-red papules with a chronic course, whereas pityriasis rosea has a herald patch and a Christmas-tree distribution.
- Trap: assuming every persistent papule is PLC without a biopsy Correct: lymphomatoid papulosis and cutaneous lymphoma are differentials, so biopsy is indicated for atypical lesions.
- Trap: choosing systemic steroids as first-line Correct: phototherapy and antibiotics are preferred, and systemic steroids are not standard here.
Frequently asked questions
What is the main difference between PLEVA and PLC?
PLEVA is acute and produces papules that necrose into haemorrhagic crusts and heal with varioliform scars. PLC is chronic and produces brown-red scaly papules that persist for months to years without necrosis. The histology and course reflect this difference.
Why is biopsy important in pityriasis lichenoides?
Biopsy is important when lesions are persistent, atypical or unresponsive, because lymphomatoid papulosis and cutaneous lymphoma can mimic pityriasis lichenoides. Histology in PLEVA shows epidermal necrosis with vasculitic change, while PLC shows parakeratosis and interface change. Clinical correlation remains essential.
Which phototherapy is used for pityriasis lichenoides?
Narrowband UVB is the phototherapy most used for pityriasis lichenoides in both acute and chronic forms. It is given several times a week over a course and is well tolerated by many patients. PUVA is an alternative in selected cases where narrowband UVB is unavailable.
Which antibiotic is used in pityriasis lichenoides?
Oral erythromycin or tetracycline is used for selected patients with pityriasis lichenoides, with the choice guided by age and local practice. Tetracyclines are avoided in young children because of tooth discolouration. Antibiotic therapy is often combined with phototherapy.