Lichen planus (LP) is a non-infectious skin condition which causes itching and the appearance of papules and plaques over various parts of the body or the mucous membranes. It can be cutaneous or oral, and at some times it may be complicated by erosions.

Diagnosis of lichen planus is based on clinical grounds, namely, the appearance of the rash in the oral cavity or on the skin. Oral lichen planus lesions are often picked up first by dentists during routine dental check-ups.

Clinical features of lichen planus

The clinical presentation of lichen planus varies with the site and type of lesion.

Cutaneous lichen planus

The diagnosis of the lesions is by picking up the characteristic six P’s, namely:

• Plaques or
• Papules which are
• Planar or flat-topped
• Purplish in color
• Polygonal and well-demarcated from surrounding skin, and
• Pruritic

Types of cutaneous lesion

Cutaneous lichen planus may occur in one of the following types:

• Linear LP: the lesions are arranged along lines, often scratches or lines produced by mechanical trauma – the Koebner’s phenomenon.
• Annular LP: the lesions are arranged in a circular fashion, or they become so by peripheral extension with central clearing. These occur on the usual sites and also on the male genital areas in some patients.
• Atrophic LP: this form is seen in the form of whitish or bluish patches, papules or plaques, with flattened lesions.
• Hypertrophic LP: also called lichen planus verrucosus, it occurs on the extremities and is extremely pruritic. It leaves scars and hyperpigmented areas behind after it resolves.
• Erosive LP: seen as waxy areas over the soles, it may be painful
• Vesiculobullous LP: this arises in the form of small or large blisters from lesions already present over the legs, lumbosacral region, or in the gluteal region.

Genital lichen planus

In women, the vulva and vagina may show any of the following lesions:

• Whitish linear or reticular striae
• A network of papules
• Erosive or ulcerative lesions

Scalp and nail lichen planus

Scalp and nail variants occur in only 10% of patients. In the scalp, it occurs as purplish lesions around a clump of hair follicles, with scaling and pruritus. It may result in scarring alopecia due to loss of hair follicles. Nail manifestations are diverse and range from:

• Ridging, thinning and detachment of the nail
• Cuticular overgrowth
• Subungual keratosis or hyperpigmentation

Oral lichen planus

Symptoms of oral lichen planus may vary. General symptoms include:

• Roughness of the buccal mucous membrane
• A burning sensation in the mouth, especially in the atrophic and erosive variants
• Sensitivity to hot or spicy food
• A metallic taste in the mouth
• Soreness or pain of the mouth

In some cases, patients with oral lichen planus present with cutaneous lesions, and the oral lesions are found only on examination. Genital lesions are present in up to 25% of women with oral lichen planus, but only up to 4% of men with similar location of lesions.

Types of oral lesion

Oral lichen planus lesions may belong to one of the following six types:

• Reticular: this is the most common and usually asymptomatic. It presents with a fine network of white lines (Wickham’s striae) which are symmetrical and found on both sides of the mouth, usually over the buccal mucous membrane.
• Erosive: these consist of irregular painful ulcers covered by a yellowish pseudomembrane of fibrin, with the white striae all around the lesions.
• Atrophic: this is usually found as an ulcer covered by a fibrinous exudate, on an erythematous background.
• Bullous: this is the least common type. It is characterized by small or large vesicles or bullae, which break open leaving a painful ulcer.
• Papular: this is a rare type, consisting of tiny raised white spots, with the characteristic white striae at the periphery.
• Plaque: the lesions appear as smooth to slightly roughened whitish patches, rather like leukoplakia, found over the tongue and the inside of the cheeks.

Differential diagnosis

In atypical cases of cutaneous lichen planus, the rash may be confused with other conditions, such as:

• Eczema
• Lichen simplex chronicus
• Pityriasis rosea
• Psoriasis

In some cases, oral lichen planus may be mistaken for:

• Oral trauma from accidental bites, or frictional keratosis
• Leukoplakia
• Candidiasis of the mouth

Diagnostic tests

In such cases, other investigations may be called for. The most common test is a 4-mm punch biopsy from an affected area, either on the skin or in the mouth. The most common pattern seen on microscopic examination of the biopsy is a “saw-tooth” pattern due to hyperplasia of the epidermis. There is a T-cell infiltrate at the dermo-epidermal junction, with vacuolar or liquefactive degeneration of the basal cells of the epidermis. The granular cell layer is thickened.

In many patients, the condition is associated with chronic hepatitis C. Thus testing for HCV is also performed in many patients, including HCV-RNA or HCV-specific CD4+ and CD8+ lymphocytes.

In vesiculobullous forms of lichen planus, the skin adjacent to the lesion may be taken for biopsy, as a direct immunofluorescence (IF) microscopy of the sample will differentiate other bullous lesions (such as pemphigus) from this condition. Direct IF shows the presence of autoantibodies bound to the skin cells.