Chapter 12 Lichenoid skin eruptions
2. What does “lichenoid” mean?
The term lichenoid has at least three commonly accepted applications/definitions:
• Originally, the term lichenoid referred to a clinical resemblance of such eruptions to lichens (complex organism consisting of a symbiotic relationship between a fungus and an alga).
• Lichen planus (LP) is the prototypical disease within this category, and eruptions sharing clinical features with LP may be described as “lichenoid.”
3. What is the most common lichenoid skin disease?
Lichen planus is a relatively common disorder, accounting for about 1% of all patient visits to dermatology clinics. The disease most often affects middle-aged adults. Although LP is thought to have no consistent gender predilection, some studies have found women to be more often affected than men. A recent meta-analysis regarding the incidence of oral lichen planus found an overall age-standardized prevalence of 1.27% (0.96% in men and 1.57% in women).
Katta R: Lichen planus, Am Fam Physician 61:3319–3324, 2000.
Carrozzo M: How common is oral lichen planus? Evid Based Dent 9:112–113, 2008.
4. What anatomic locations are most often affected by Lichen planus?
LP may affect both the skin and mucosa. Examination of both areas is essential when the diagnosis of LP is suspected. The frequency of involvement for these areas is somewhat controversial. In general, patients with mucosal disease may not demonstrate skin lesions, but 50% or more of patients with cutaneous disease will demonstrate mucosal lesions. Flexural areas, such as the wrists and ankles, are often involved. Other sites of preferential involvement include the neck, buttocks, sacrum, anogenital region, penis, and buccal or vaginal mucosa.
5. Describe the characteristic primary skin lesions of Lichen planus.
LP is a disease characterized by “P-words”:
• Papules
Primary lesions of the skin are 1 to 5 mm, flat-topped, violaceous, shiny papules (Fig. 12-1). While papules are often clustered, individual lesions tend to be discrete, with angulated (polygonal) borders. Wickham’s stria, a lacy white network present on the surface of the papules, is often of great diagnostic value.
6. What are the characteristic oral findings of Lichen planus?
Mucosal lesions of LP differ from cutaneous lesions through demonstration of Wickham’s stria in the absence of a papular component. A white, reticulated, “netlike” pattern is often present upon the buccal mucosa, the tongue, or other mucosal surfaces (Fig. 12-2). Other mucosal forms may be ulcerative. Some experts believe that some cases of oral LP may be associated with mercury-containing dental amalgams, although the evidence is not conclusive, and still others believe this is a separate category of disease, more aptly termed a mercury-associated lichenoid stomatitis.
Figure 12-2. Lichen planus, showing reticulated leukoplakia of the buccal mucosa.
(Courtesy of James E. Fitzpatrick, MD.)
Dissemond J: Oral lichen planus: an overview, J Dermatol Treat 15:136–140, 2004.
Bruce AJ, Rogers RS 3rd: Lichenoid contact stomatitis, Arch Dermatol 140:1524–1525, 2004.
7. Describe the isomorphic response of Lichen planus.
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).
8. What causes Lichen planus?
The cause of LP is unknown. Etiologic hypotheses include hypersensitivity reactions, viral infection (particularly hepatitis C), or autoimmune mechanisms. Case reports have linked LP to viral hepatitis, neurologic disease, and severe psychic trauma. Other autoimmune diseases such as vitiligo, inflammatory bowel disease, and autoimmune thyroiditis are seen with increased frequency in those with LP. Lichenoid eruptions (otherwise identical to idiopathic LP) may be seen as a reaction to drugs or as a manifestation of graft-versus-host disease following allogeneic bone marrow transplantation. Oral disease and, to a lesser degree, cutaneous LP have been associated with hypersensitivity to dental amalgams. In actuality, most LP occurs in otherwise healthy people without an identifiable cause.
9. What are the less common presentations of Lichen planus?
Nail changes occur in about 10% to 15% of patients and include longitudinal ridging, irregular pitting, nail plate splitting, nail loss, and pterygium formation with severe onychodystrophy, including “20-nail dystrophy” (Fig. 12-4). Desquamative vaginitis may occur. Clinical and histologic variants of LP include annular (Fig. 12-5), hypertrophic, ulcerative, vesiculobullous, follicular, and actinic induced. LP may also involve the scalp, yielding a scarring alopecia known as lichen planopilaris.
