Pityriasis lichenoides: pathophysiology, classification, and treatment.

Area of Science:

• Dermatology
• Pathology
• Immunology

Background:

• Pityriasis lichenoides (PL) is an uncommon, acquired skin condition with diverse clinical presentations and diagnostic challenges.
• Its spectrum includes pityriasis lichenoides et varioliformis acuta (PLEVA), pityriasis lichenoides chronica (PLC), and the severe febrile ulceronecrotic Mucha-Habermann disease (FUMHD).
• Understanding PL is critical due to its potential to evolve into cutaneous lymphoma or life-threatening ulceronecrotic forms.

Observation:

• PLEVA presents as acute-to-subacute red papules that evolve into polymorphic lesions with potential scarring.
• PLC manifests as gradual, small red-to-brown maculopapules with scaling, characterized by relapsing courses.
• FUMHD is a severe, acute eruption of purpuric and ulceronecrotic plaques with systemic involvement and high mortality.

Findings:

• Histopathology typically shows a dermal lymphocytic infiltrate, epidermal changes, and keratinocyte necrosis, varying in severity across PL variants.
• The exact pathogenesis remains unclear, with theories including infectious or drug hypersensitivity versus lymphoproliferative disorders.
• Successful treatment of PLC was achieved with narrow-band UVB phototherapy, alongside standard therapies like antibacterials and corticosteroids for PLEVA.

Implications:

• Accurate diagnosis and classification of PL variants are essential for appropriate management.
• Timely and aggressive treatment, especially for FUMHD, is crucial to prevent mortality and severe sequelae.
• Further research into PL pathogenesis may lead to more targeted and effective therapeutic strategies.