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Lichenoid Skin Eruptions

»	How do lichenoid eruptions differ from other papulosquamous conditions?
»	What does “lichenoid” mean?
»	What is the most common lichenoid skin disease?
»	What anatomic locations are most often affected by Lichen planus?
»	Describe the characteristic primary skin lesions of Lichen planus.
»	What are the characteristic oral findings of Lichen planus?
»	Describe the isomorphic response of Lichen planus.
»	What causes Lichen planus?
»	What are the less common presentations of Lichen planus?
»	How is 20-nail dystrophy related to Lichen planus?
»	Is Lichen planus associated with systemic diseases?
»	What is the prognosis of Lichen planus?
»	What is the primary symptom of Lichen planus?
»	Describe the characteristic histopathologic features of classic Lichen planus.
»	How is lichen planus treated?
»	What conditions enter the differential diagnosis of an “Lichen planus-like” eruption?
»	Are Lichen planus and systemic lupus erythematosus related?
»	Are Lichen planus and bullous pemphigoid related?
»	Why is graft-versus-host disease a consideration in Lichen planus-like eruptions?
»	Describe the primary lesion of lichen nitidus.
»	What are the other clinical features of lichen nitidus?
»	Does lichen nitidus demonstrate a lichenoid infiltrate upon biopsy?
»	What is lichen striatus?
»	Discuss the natural history and prognosis of lichen striatus.
»	What is lichen simplex chronicus?
»	How is lichen simplex chronicus treated?

Describe the isomorphic response of Lichen planus.

Lichen planus with Koebner phenomenon. Note the linear distribution of secondary lesions that develop in sites of excoriation. (Courtesy of Whitney A. High, MD.)

Fig. 12.3 Lichen planus with Koebner phenomenon. Note the linear distribution of secondary lesions that develop in sites of excoriation. (Courtesy of Whitney A. High, MD.)

The isomorphic response (Koebner phenomenon) refers to development of new lesions as a response to external trauma. This phenomenon is characteristic of both LP and psoriasis, among other more rare conditions. In LP, linear aggregates of typical papules may be induced by scratching or rubbing (Fig. 12-3).