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OTHER LICHENOID CONDITIONS
Several other conditions are usefully discussed here. Most are clinically lichenoid (i.e. consisting of flat-topped papules or small plaques); some also have lichenoid histology.

Fig. 8.24 Lichenoid reaction due to dental amalgam, which produces a coarser pattern of white streaks (compare with Fig.8.22). When the mouth was closed, this lesion was in close proximity to a filled tooth, just visible in the upper jaw. The patient had positive patch tests to mercurial chemicals.

Fig. 8.25 Ulcerative oral lichen planus (LP). (a) LP causing buccal erosion. By contrast to most oral LP, this pattern often causes significant soreness and difficulty eating. When it occurs as part of the eruption of cutaneous LP, it may persist long after the skin lesions have resolved. (b) Ulcerated LP of the tongue. The dorsal surface of the tongue is purplish in color, with myriad small, white striae and extensive ulceration.

Fig. 8.26 Lupus erythematosus of the lips may be more scaly and scarring, but in some patients produces prominent lichenoid change, as shown here (this patient had previous discoid lupus erythematosus on the cheek, and oral biopsies also favored this diagnosis).

Lichen nitidus
This is an uncommon disorder, of unknown etiology, which occurs predominantly in young adults, and which has a body site distribution similar to that of LP. However, the individual lesions are tiny (pinhead-sized), domed papules with a typical orange-brown color (Fig.8.27). They are usually asymptomatic, not very visible, and no treatment is usually required. Koebner reactions are common (see Fig.8.27a). Involvement of the palm and sole, or of the nails (Fig.8.28), is extremely uncommon but may be relatively refractory and disabling due to hyperkeratosis at these sites.

Fig. 8.27 Lichen nitidus. (a) Small, orange-brown papules demonstrating the Koebner reaction. (b) Lichen nitidus on the hand of an African-Caribbean patient. In dark-colored skin, the papules of lichen nitidus look white and shiny.

Fig. 8.28 Lichen nitidus of the nail. Punctate red lesions are visible in the lunula, and nail pits. The patient had severe palmoplantar involvement with marked hyperkeratosis, a rare variant, and was treated with systemic retinoids.

Lichen striatus
This is an uncommon but characteristic eruption. It has an acute onset, and most commonly occurs as a solitary, long, thin lesion running down
a limb (Fig.8.29). It follows developmental lines known as lines of Blaschko. Occasionally, multiple lesions or truncal lesions may occur. In
a minority of cases, there appears to be a temporal link with a recent infection, especially in children, and sequential development of lichen striatus in siblings has been reported, which supports the concept of an infectious trigger.
    The close-up morphology may be strikingly lichenoid, but few patients report significant symptoms. A topical corticosteroid may be required to reduce the inflammatory component, and resolution usually occurs over a period of some months.

Fig. 8.29 Lichen striatus. This is most common in children (a) but can occur in adults (b,c). Both (a) and (b) show a narrow band extending down the posterior aspect of the leg. Limb lesions of this disorder are usually solitary, whereas truncal lesions may be multiple and more arciform in distribution, following Blaschko lines (c). (Panel a courtesy of Dr. L. Barco.)

Frictional lichenoid eruption
This is a relatively uncommon disorder, but probably underdiagnosed, as it is often asymptomatic. It is most frequent in boys in the 5–10-year age group, and consists of clusters of tiny lichenoid papules, which occur predominantly over bony prominences on the limbs (Fig.8.30). There is often an atopic background. Treatment is with emollients.

Fig. 8.30 Frictional lichenoid eruption. Grouped, small, flat-topped papular lesions on the elbow, a typical site.

Lichen spinulosa
This poorly defined disorder resembles keratosis pilaris but occurs as closely grouped, spiky lesions, usually in children (Fig.8.31). Treatment
is with emollients if required.

Fig. 8.31 Lichen spinulosa. Closely grouped, spiky, keratotic lesions resembling keratosis pilaris but with a more discrete arrangement of lesions.

Keratosis lichenoides chronica (Nékam disease)
This is a rare disorder, characterized by keratotic lichenoid papules and plaques with a streaky linear or reticulate patterning (Fig.8.32). Any body site may be affected. The facial rash resembles seborrheic dermatitis.

Fig. 8.32 Keratosis lichenoides chronica (Nékam disease). Typical reticulate and linear arrangement of chronic inflammatory keratotic lesions. (Courtesy of Gerald Weinstein.)

Erythema dyschromicum perstans (ashy dermatosis)
An uncommon disorder, in which there are poorly demarcated blotchy areas of dermal pigmentation, typically with a slate-gray color, and usually occurring on the trunk in children or young adults (Fig.8.33). In some cases, there is some preceding erythema and histologic evidence of basal cell vacuolization, but clinically there are no discrete lesions as seen in LP. It is the histology that resembles resolving LP; some view this as a variant of LP rather than as a separate disorder. Topical treatments are unhelpful.

Fig. 8.33 Erythema dyschromicum perstans. The reason for the alternative name, ashy dermatosis, is apparent from the grayish color of the lesions. The poorly defined blotchy appearance on the trunk (a) and arms (b), as seen here, is typical.

Annular lichenoid dermatitis of youth
It is uncertain whether this recently described condition is a specific entity. Twenty-three patients, mean age 10 years, were described with an annular lichenoid dermatitis, with central hypopigmentation, resembling mycosis fungoides, morphea, or annular erythema. Treatment was with topical or oral steroids, or with phototherapy.

Graft-versus-host disease
Graft-versus-host disease (GVHD) is a skin eruption that occurs in recipients of allogeneic tissues, in which donor immune cells attack host tissues due to histoincompatibility. It is discussed in more detail in Chapter.12. Chronic GVHD may cause a rash resembling LP, including oral lesions.
Drug-induced lichen planus or lichenoid eruption and other exogenous causes
Drugs may cause an eruption that is similar to LP (Fig.8.34). A list of likely medications and external agents that may cause a lichenoid eruption or LP-like contact dermatitis is given in Table 8.4; a more detailed list of the drug triggers is provided in Chapter 18, along with a list of issues that contribute to difficulty in diagnosis.

Fig. 8.34 Examples of drug-induced lichenoid eruptions. Some occur due to a drug in isolation, such as this eruption on the foot (a) due to a beta-blocker. Acral sites are often affected in lichenoid drug eruptions. In other cases, the reaction may be photolichenoid, occurring on sun-exposed skin, such as the eruptions in (b) and (c), which were both due to the antimalarial drug hydroxychloroquine. (Panel a courtesy of Dr. G. Dawn.)

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