Lichen Planus

Lichen planus is a pruritic, papular eruption characterised by its violaceous colour and polygonal shape, sometimes with a fine scale. It is most often found on the flexor surfaces of the upper extremities, genitalia and on the mucous membranes. The cause of lichen planus is unknown but it is most likely an immunologically mediated reaction.¹

• Can occur at any age, but is uncommon in the very young or elderly.
• Can be precipitated by trauma (Koebner phenomenon).
• Immunologically mediated (perhaps triggered by a virus) and can occur in families.
• Associated with primary biliary cirrhosis.

• Onset is usually acute, affecting the flexor surfaces of the wrists, forearms and legs.
• The typical lesion is an intensely itchy 2-5 mm red or violet shiny flat-topped papule with white streaks ('Wickham's striae').
  
  
  
  
  
  
• Blisters occasionally occur.
• As the papules clear they may be replaced by brown discolouration (especially in the dark skinned). Lesions may occur on any part of the body surface, but most commonly on the front of the wrists, flexor aspects of the forearms, genitals, lumbar region and the ankles and shins (where lesions are most commonly hypertrophic, frequently very itchy and may ulcerate).
• It may appear in linear form, following the lines of trauma (Koebner phenomenon). Rarer forms of lichen planus include atrophic, ulcerative and hypertrophic forms, which tend to be more persistent and resistant to treatment.
• On the palms and soles the papules are firm and yellow.
• Mucous membranes are commonly affected:
  • Classically white slightly raised lesions with a trabecular, lacy appearance on the inside of the cheeks.
    
    
    
    
    
    
  • The mucous membrane lesions are often asymptomatic but can be very painful and difficult to treat. Oral lichen planus may cause sensitivity to heat.
  • Lesions may also be found on the genitalia, anus, larynx and very rarely on the tympanic membrane or oesophagus (where it can present as dysphagia and cause benign strictures).
• Nails are involved in up to 10% of patients: longitudinal lines and linear depressions of the nail plate, severe dystrophy and complete destruction of the nail bed may occur.
• The scalp is usually spared but lichen planus affecting the scalp may cause permanent scarring alopecia.

Lichen planus can usually be diagnosed clinically and histology is not often required. Skin biopsy is characteristic:

• There is a "saw-tooth" pattern of epidermal hyperplasia and vacuolar alteration of the basal layer of the epidermis along with an intense upper dermal band-like lymphohistiocytic infiltrate (mainly T-cells).
• This initially develops around blood vessels at the dermal/epidermal junction and disrupts the basal epidermal layer.
• There is a reduced number of melanocytes in this region and focal areas with a thicker granular layer and infiltrate (the 'Wickham's striae').
• Direct immunofluorescence shows globular deposits of IgM (occasionally IgG and IgA).

• Drug eruption (lichenoid), e.g. thiazides, anti-malarials, gold
• Eczema
• Psoriasis
• Candidiasis
• Cutaneous graft-versus-host-reaction
• Discoid lupus erythematosus
• Granuloma annulare
• Lichen amyloidosis
• Leukoplakia
• Lichen sclerosus
• Pemphigus
• Pleomorphic (small cell) T-cell lymphoma
• Sarcoidosis
• Basal cell carcinoma
• Toxoplasmosis

• Treatment is not always needed. Skin lichen planus may resolve spontaneously within a year, although mucous membrane lichen planus may be more persistent and resistant to treatment.
• If drugs are suspected as the cause, they should be stopped.
• Symptomatic treatment for itching, e.g. moderately potent topical steroids (intra-lesional steroid injections may be beneficial for patients with severe and persistent itch) and sedating antihistamines.
• Extensive cases may merit systemic steroids (30 mg of oral prednisone for ten days) to lessen the itch and often clear up the lichen planus completely (although it may recur).²
• There is little evidence for the benefit of any specific treatment for oral lichen planus.³ However topical corticosteroids (e.g. steroid lozenges) have been shown to be the most effective treatment.⁴
• Ciclosporin A is effective at low dose (topical ciclosporin has also been used for vulval disease, but its efficacy is not proven).⁵
• PUVA (psoralen with UVA radiation) may help reduce pruritus and help to clear the lichen planus.
• Systemic retinoids (e.g. isotretinoin) have been used for resistant disease, but the condition usually relapses after treatment, necessitating maintenance therapy.
• Levamisole has been used with some success in oral lichen planus.⁶

• Oral lichen planus carries a very small risk of malignant change.
• Squamous cell carcinoma develops in 0.4% to 2% of cases of oral lichen planus especially when it has been present for more than 5 years.
• Hypertrophic lesions may leave residual hyperpigmentation.¹

• Spontaneous resolution usually occurs over a period of 3 months to 2 years.
• The degree of pruritus tends to decrease with time.