White : Diseases of the Skin - Lichen Planus and Lichenoid Disorders

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Gary M. White & Neil H. Cox

Diseases of the Skin

8	Lichen Planus and Lichenoid Disorders

ORAL LICHEN PLANUS AND THE ORAL LICHENOID
ERUPTION

Etiology and pathogenesis

The oral lichenoid eruption is a less speciﬁc entity compared with LP of the skin. It is best considered as a reaction pattern of the oral mucosa to a variety of insults, including LP itself, contact allergy (especially to mercury in dental amalgam), trauma, and other inflammatory dermatoses (e.g.
oral lupus erythematosus may look very lichenoid). Some cases related
to dental ﬁllings appear to be related to corrosion of amalgam or to use of mixed metal materials, creating a galvanic effect. Even patients in whom mercury allergy cannot be demonstrated may beneﬁt from removal of ﬁllings.

Clinical features
Oral lichenoid reactions resemble the Wickham’s striae seen in the surface of skin lesions of LP. Fine, white streaking and reticulate patterning is apparent in the mouth, and is usually most apparent on the buccal mucosa (Fig.8.22). However, any part of the mouth can be affected, including the gums, lips, palate, and tongue (Fig.8.23).
The most elegant, ﬁne, lace-like pattern is seen in true LP (see Fig.8.22), most other lichenoid reactions being rather coarser in pattern (Fig.8.24). Erosive and pigmented LP also occur in the mouth (Fig.8.25).
The site of lesions may give clues to the etiology. Repetitive trauma due to trapping of the buccal mucosa between the upper and lower molars produces a linear lichenoid lesion (bite line). Reactions to mercury in dental amalgam or other dental ﬁlling reactions are usually most prominent in proximity to ﬁlled teeth. Lupus erythematosus may affect the lips (Fig.8.22) in isolation or in patients with discoid or systemic disease,
and may be associated with lichenoid eruptions at other intraoral sites (Ch.13).

Table 8.3 DIFFERENTIAL DIAGNOSIS OF SOME MORPHOLOGIC AND SITE-SPECIFIC VARIANTS OF LICHEN PLANUS
Variant	Differential diagnoses^a
Drug- or contact-induced lichenoid reaction	Usually more psoriasiform clinically; mixed inﬁltrate, including eosinophils histologically
Lupus erythematosus distinguish the two	Not usually clinically confused, but may be difﬁcult at some sites; direct immunofluorescence of biopsy may
Erythema dyschromicum perstans (ashy dermatosis)	Resembles healing LP, may be a variant of LP
Lichen nitidus	May resemble guttate or follicular LP clinically; histologically, inﬁltrate is tightly compacted and often granulomatous
Keratosis lichenoides chronica	Clinically distinctive (also known as Nékam disease)
Lichen planus pemphigoides	Extreme basal epidermal degeneration in LP causes clefts (Max–Joseph spaces) that resemble the subepidermal bullae of lichen planus pemphigoides
Lichenoid actinic keratosis	Usually solitary, clinically a rather flat actinic keratosis; unlikely to cause a diagnostic problem if clinical and pathologic features are considered together
Lichen striatus	Clinically distinctive (see text for details)
Syphilis	May have lichenoid histology (may include plasma cells); secondary syphilis is in the clinical differential of generalized or palmoplantar LP
Lichenoid mycosis fungoides	A rare variant, usually plaques rather than the more isolated lesions of LP; histologically has epidermal component, atypical lymphocytes
Graft-versus-host disease	One pattern of this reaction, usually apparent from the clinical situation

Investigations
Biopsy may be required to exclude leukoplakia and conﬁrm that the eruption is benign lichenoid change, especially if the changes are unilateral or asymmetric. Chronic candidal infection may require swabs and biopsy to distinguish it from oral lichenoid change. Special techniques such as immunofluorescence examination of biopsy specimens may be required
in cases in which there is suspicion of mucous membrane pemphigoid,
in which resolved blisters may leave a residual lichenoid change. Longstanding, especially erosive, oral LP carries a small risk of neoplastic degeneration and should be biopsied in cases where lesions deteriorate or become thickened.
In patients with oral lichenoid change and without skin signs of LP, about 20% have a contact allergy, which can be identiﬁed by patch testing. Lichenoid oral contact allergy can be to flavoring agents such as balsams or cinnamaldehyde, but most are to mercury in dental amalgam.

Differential diagnosis
This is listed in Table 8.3.

Treatment
Many patients with oral lichenoid appearance, due to LP or other causes, have no symptoms. In such instances, no treatment is required, although follow-up has been advised due to the risk of subsequent oral squamous carcinoma.

Fig. 8.22 Buccal lichen planus showing the typical ﬁne lace-like pattern

     In symptomatic patients, topical corticosteroids may be administered as ointments, dental pastes, aqueous sprays, or dental lozenges. Non-steroidal antiinflammatory mouthwashes, and antiseptic mouthwashes, may also be helpful. Topical ciclosporin as a mouthwash produces variable beneﬁt, but may be limited by lack of penetration into the mucosa. Topical tacrolimus can be beneﬁcial, but the response is not reliable in the author’s experience.
    Resistant lesions may require intralesional steroid injection, or systemic treatment as for LP. The combination of oral and genital or perineal LP, without lesions elsewhere, seems to be a particularly troublesome and resistant form of this disease.
    In patients with allergy to mercury in dental ﬁllings, most improve
after their ﬁllings are removed and replaced with composite materials. However, the release of mercury during the procedure, and the physical handling of the mouth, may cause transient deterioration in symptoms.

Fig. 8.23 Patterns of lichen planus (LP) affecting the mouth. (a) LP of the gingival mucosa, again with typical ﬁne, white striae. (b) LP of the lip. In this case, there are quite irregular teeth, which may have caused a degree of local trauma. In the absence of LP elsewhere, this should be biopsied to exclude leukoplakia. (c) Erosive LP of the palate. This was associated with perianal and genital LP, and was unresponsive to a wide range of topical and systemic medications, including ciclosporin, azathioprine, and thalidomide. (d) Pigmented LP in the mouth causes diagnostic concern but has no particular signiﬁcance. It may occur in lichenoid drug eruptions. (e) Annular lesions of LP on the tongue may be confused with migratory glossitis or candidiasis. Secondary syphilis should also be considered. (f) LP of the lateral tongue border, a pattern that closely resembles leukoplakia and requires a biopsy.

Practice points

  •   If oral lichen planus (LP) is very localized, consider the possibility o f reaction to amalgam ﬁllings.

  •   Oral LP may persist long after the cutaneous component has resolved.

  •   Patients with erosive oral LP justify review due to the risk of malignancy.