Lichen planus describes a condition in which the lesions are:
• Purplish in colour
• Polygonal in outline
• Planar or flat-topped papules
The cause is unknown but some gross forms of lichen planus may occur in association with diseases in which there is a profound immunological abnormality such as myasthenia gravis with thymoma, and with graft-versushost disease. It is also seen with autoimmune chronic liver disease, e.g. primary biliary cirrhosis or chronic active hepatitis. Oral disease has been associated with amalgams in dental fillings. Lichen planus-like reactions occur with certain drugs such as sulphonamides (most commonly taken as sulphasalazine), sulphonylureas, methyldopa, thiazide diuretics and J3-blockers. Patients with rheumatoid arthritis treated by agents that alter immune function, such as antimalarials, gold, levamisole or penicillamine, may also develop lichen planus-like lesions or lichenoid rashes.
This is characteristic, with the epidermis showing hyperkeratosis, and a marked chronic lymphocytic infiltrate is seen at the epidermodermal junction. This infiltration consists principally of T cells and suggests an immunological reaction to an epidermal antigen.
The distribution of the lesions is peripheral, involving the wrists and ankles, usually symmetrically. The genitalia, scalp or nails are less frequently involved; with chronic disease the scarring that may occur can permanently damage the growth of hair or nails. Scarring may also accompany the less frequent annular patterns of the disease. Liner lesions may follow trauma or scratching (Koebner phenomenon) or may occur in children in a naevoid fashion along a limb. Trauma to the mucosa overlying the bite margin in the mouth commonly induces involvement at this site, producing distinctive pale white linear markings or patterns. Erosive changes may also be seen on the buccal mucosa or tongue or female genitalia.
The presence of Wickham’s striae-fine white lacy patterning coursing over the papule-helps to distinguish this disease. Postinflammatory hyperpigmentation is also a useful diagnostic sign if the disease is beginning to fade at the time of first presentation.
Untreated, common patterns of the disease may last for12-18 months. Hypertrophic lesions on the legs or annular patterns may be rather more persistent; recurrence may occur in about one-fifth of cases.
Widespread acute disease is often associated with intractable itching and this may require oral prednisolone for control, given over several months. Less acute disease may be managed with the topical application of potent corticosteroids together with a sedative antihistamine given at night to control the itching.
This is a self-limiting non-recurrent scaling maculopapular eruption occurring principally in children and young adults. The disease is less common in the summer, and current epidemiological evidence suggests an infectiv cause, most probably viral. Drugs, e.g. penicillamine, gold, may induce identical clinical features. Males and females are equally affected.
Commonly, a larger and more conspicuous lesion, 2-6 cm in diameter, will precede the more widespread rash by up to 10 days (the herald patch). Individual lesions, occurring predominantly on the trunk, are reddishbrown in colour, macular, scaled and discrete. They often course over the chest wall following the line of the ribs in a linear fashion. The proximal limb girdle is also affected but the face and scalp are rarely involved. Individual lesions, especially over the neck, may show a collarette, i.e. a border composed of a rim of scales that point towards the centre. Florid inflammatory papules may occasionally be seen, and individual lesions may be rather more hyperkeratotic on black or Asian skins. The eruption is only mildly pruritic and usually clears in 6-8 weeks without treatment.
Constitutional upset may be noticed prior to the onset of the rash or within the first few days of its appearance. This should help to distinguish the condition from secondary syphilis which it may closely resemble but in which systemic features are usually more severe.