Lichen planus

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Overview
Lichen planus is an inflammatory disease that affects the skin and the oral mucosa.

Cause
The cause of lichen planus is not known; however, there are cases of lichen planus-type rashes (known as lichenoid reactions) occurring as allergic reactions to medications for high blood pressure, heart disease and arthritis. These lichenoid reactions are referred to as lichenoid mucositis (of the mucosa) or dermatitis (of the skin). Lichen planus has been reported as a complication of chronic hepatitis C virus infection and can be a sign of chronic graft-versus-host disease of the skin. It has been suggested that true lichen planus may respond to stress, where lesions may present on the mucosa or skin during times of stress in those with the disease. Lichen planus affects women more than men (at a ratio of 3:2), and occurs most often in middle-aged adults. Lichen planus in children is rare.

Clinical features
The typical rash of lichen planus is well-described by the "5 P's": well-defined pruritic, planar, purple, polygonal papules. The commonly affected sites are near the wrist and the ankle. The rash tends to heal with prominent blue-black or brownish discoloration that persists for a long time. Besides the typical lesions, many morphological varieties of the rash may occur. The presence of cutaneous lesions is not constant and may wax and wane over time. Oral lesions tend to last far longer than cutaneous lichen planus lesions.

Oral lichen planus may present in one of three forms.
 * The reticular form is the most common presentation and manifests as white lacy streaks on the mucosa (known as Wickham's striae) or as smaller papules (small raised area). The lesions tend to be bilateral and are asymptomatic.  The lacy streaks may also be seen on other parts of the mouth, including the gingiva (gums), the tongue, palate and lips.
 * The bullous form presents as fluid-filled vesicles which project from the surface.
 * The erosive form presents with erythematous (red) areas that are ulcerated and uncomfortable. The erosion of the thin epithelium may occur in multiple areas of the mouth, or in one area, such as the gums, where they resemble desquamative gingivitis.  Wickham's striae may also be seen near these ulcerated areas.  This form may undergo malignant transformation.

The microscopic appearance of lichen planus is pathognomonic for the condition
 * Hyperparakeratosis with thickening of the granular cell layer
 * Development of a "saw-tooth" appearance of the rete pegs
 * Degeneration of the basal cell layer
 * Infiltration of inflammatory cells into the subepithelial layer of connective tissue

Lichen planus may also affect the genital mucosa - vulvovaginal-gingival lichen planus. It can resemble other skin conditions such as atopic dermatitis and psoriasis.

Rarely, lichen planus shows esophageal involvement, where it can present with erosive esophagitis and stricturing. It has also been hypothesized that it is a precursor to squamous cell carcinoma of the esophagus.

Clinical experience suggests that Lichen planus of the skin alone is easier to treat as compared to one which is associated with oral and genital lesions.

Differential Diagnosis
The clinical presentation of lichen planus may also resemble other conditions, including:


 * Lichenoid drug reaction
 * Discoid Lupus Erythematosus
 * Chronic Ulcerative Stomatitis
 * Pemphigus Vulgaris
 * Benign Mucous Membrane Pemphigoid
 * Oral leukoplakia
 * Frictional keratosis

A biopsy is useful in identifying histological features that help differentiate lichen planus from these conditions.

Treatment
Currently there is no cure for lichen planus but there are certain types of medicines used to reduce the effects of the inflammation. Lichen planus may go into a dormant state after treatment. There are also reports that lichen planus can flare up years after it is considered cured.

Medicines used to treat lichen planus include:
 * Oral and topical steroids.
 * Oral retinoids
 * immunosuppressant medications
 * hydroxychloroquine
 * tacrolimus
 * dapsone

Lichen planopilaris
Lichen Planopilaris is the specific name given to lichen planus on the scalp that may cause permanent, scarring alopecia. If left untreated the scarring will cause permanent hair loss. The Cicatricial Alopecia Research Foundation is a non-profit organization that provides support and resources for people with lichen planopilaris.

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