What causes Pityriasis lichenoides and how is it treated?

Pityriasis Lichenoides: Causes and Treatment

Pityriasis lichenoides is likely caused by an immune-mediated response to infectious triggers, with treatment primarily consisting of narrow-band UVB phototherapy, oral erythromycin, or methotrexate depending on disease severity.

Etiology

Pityriasis lichenoides (PL) is an uncommon acquired spectrum of skin conditions with unclear etiology, but several theories exist:

• Infectious triggers: Evidence suggests associations with:

  • Epstein-Barr virus (EBV) 1
  • Toxoplasma gondii 1
  • HIV 1
  • Other viral or bacterial agents

• Immune-mediated process: PL is considered an inflammatory disorder with:

  • T-cell mediated immune response 2
  • Possible hypersensitivity reaction to infectious agents 2

• Lymphoproliferative disorder: Some evidence suggests PL may represent a benign lymphoproliferative condition 2, 3

• Medication-induced: Similar to lichenoid reactions, some cases may be triggered by medications 4

Clinical Presentation

Pityriasis lichenoides exists on a spectrum with three main variants:

1. Pityriasis lichenoides et varioliformis acuta (PLEVA):

   • Acute-to-subacute eruption
   • Multiple small red papules evolving into polymorphic lesions
   • May leave hyper/hypopigmentation and varicella-like scars 2

2. Pityriasis lichenoides chronica (PLC):

   • More gradual onset
   • Small red-to-brown flat maculopapules with mica-like scale
   • Longer periods of remission 2

3. Febrile ulceronecrotic Mucha-Habermann disease (FUMHD):

   • Acute severe generalized eruption
   • Purpuric and ulceronecrotic plaques
   • Systemic involvement with up to 25% mortality rate
   • Dermatologic emergency 2

Treatment Approach

First-Line Treatments

1. Phototherapy:

   • Narrow-band UVB: Most effective first-line treatment with clearance rates between 70-100% 5
   • Better safety profile than PUVA, especially for children 3, 5

2. Oral antibiotics:

   • Erythromycin: Clearance rates of 66-83% 5
   • Well-tolerated in children 3

3. Topical therapy:

   • Ultrapotent topical corticosteroids (similar to treatment for lichen planus)
   • Can be used as adjunctive therapy 4

Second-Line Treatments

1. Methotrexate:

   • Reported clearance rates up to 100% in small studies 5
   • Reserved for more severe or recalcitrant cases

2. Combination therapies:

   • Antibiotics plus phototherapy
   • Topical corticosteroids plus systemic treatment

Treatment for FUMHD (Severe Variant)

• Aggressive immunosuppressant/immunomodulating therapy
• Intensive supportive care
• Immediate hospitalization due to high mortality risk 2

Monitoring and Follow-up

• Long-term follow-up recommended due to rare reports of progression to cutaneous T-cell lymphoma 3
• Monitor for disease recurrence, as PL often follows a relapsing course 2
• Evaluate for resolution of lesions and potential sequelae (scarring, pigmentary changes)

Special Considerations

• Pediatric patients: PL occurs with an average age of onset of 6.5 years with slight male predominance (61%) 3
• Treatment selection: Consider age, disease extent, and variant when selecting therapy
• Disease course: Most cases follow a benign course but may have prolonged duration with relapses

Treatment Algorithm

1. Mild to moderate disease:

   • Start with narrow-band UVB phototherapy (2-3 sessions per week)
   • If phototherapy is unavailable, use oral erythromycin (30-50 mg/kg/day in children; 1g/day in adults)
   • Add topical corticosteroids for symptomatic lesions

2. Severe or recalcitrant disease:

   • Consider methotrexate (low-dose regimen)
   • Combination therapy with phototherapy and antibiotics

3. FUMHD variant:

   • Immediate hospitalization
   • Aggressive immunosuppression (systemic corticosteroids, cyclosporine)
   • Intensive supportive care

While PL can be challenging to treat and may follow a relapsing course, most patients respond well to therapy with appropriate selection and duration of treatment.