Table of Contents   This Chapter   All Chapters

THE LICHENOID ERUPTION

The lichenoid eruptions are those that resemble lichen planus. However, the term is used for both clinical and for histologic resemblance. Clinically, lichenoid conditions all tend to have flat-topped and rather shiny lesions, often with a violaceous or brownish color. However, some lesions that carry the term lichen (such as lichen sclerosus) bear little clinical resemblance to lichen planus, although they have a strong histologic resemblance. The term lichenoid, as applied to the histologic pattern, describes a band-like interface dermatitis; the features of this reaction pattern are listed in Table 8.1 and some disorders that may have lichenoid histology are listed in Table 8.2.
    Conversely, some disorders having names that include the term lichen or lichenoid, on the basis of flat or flat-topped lesions, such as lichen aureus (a capillaropathy, Ch.14) or pityriasis lichenoides (Ch.33), are histologically distinct. Other disorders may be clinically very similar to lichen planus, having flat, purplish lesions, but are different in behavior and pathology; the rare condition of paraneoplastic pemphigus is an example (Ch.16).
    Lichen sclerosus does have lichenoid histology, especially in early lesions, but is discussed elsewhere in accordance with its two main clinical presentations, either as genital lesions (Ch.20) or as areas of altered pigmentation and atrophy (Ch.22).
    Most of the lichenoid pathologic features are present to varying degrees in lupus erythematosus. Clinically, distinguishing lichen planus from discoid lupus erythematosus (Ch.13) is not usually difficult, but at some sites in isolation (notably scalp, nail folds, and oral mucosa) the clinical and pathologic features may both be very similar. Direct immunofluorescence of a skin biopsy usually helps to resolve this issue, as deposition of IgG and complement C3 at the dermo–epidermal junction or in cytoid bodies favors lupus erythematosus, whereas prominent fibrin deposition favors lichen planus. IgM in cytoid bodies or at the dermo–epidermal junction occurs in both disorders

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.