Lichen planus is a chronic inflammatory disease involving the skin, hair follicles, nails and mucous membranes of unknown origin, mostly occurring in middle-aged people, with a characteristic rash manifesting as purplish-red polygonal flat papules and plaques, most often on the wrists, forearms, distal lower extremities and presacral area, with self-induced pruritus. In some patients, the rash is associated with oral medications, such as thiazide diuretics and antimalarials. Clinically the disease includes many types, such as linear, annular, hypertrophic, atrophic, maculopapular, pigmented, ray, and hairy lichen planus. Histological manifestations include liquefied basal cell degeneration and lymphocytic banding in the superficial mid-dermis. The etiology of lichen planus is not yet clear, but it is generally considered to be related to mental, genetic, immune, infectious, and drug factors. In Chinese medicine, the onset of lichen planus is associated with Qi stagnation and blood stasis, siltation of blood on the skin, siltation of blood into heat and wind, or external exposure to wind. Anxiety and depression are both associated with liver stagnation and qi stagnation. Some patients exhibit spleen deficiency, kidney deficiency, skin and yang deficiency, so that the flow of qi and blood is not smooth, kidney yang deficiency, cold obstruction of blood stagnation, etc. are also related to the onset of the disease. Clinical manifestations The disease manifests as small, purplish-red, polygonal flat papules with a shiny surface and visible white reticular stripes. The rash is mostly distributed on the flexors of the wrist and forearm, the back of the hand, forearm, neck, and sacrococcygeal area, and may form a new rash with a linear distribution at the scratching site (isomorphic reaction). Patients may feel itchy and the rash may fade after several months to years, with some pigmented patches remaining. Lichen planus can involve mucosal areas, most often in the oral cavity, manifesting as heavy white reticular lines on the mucous membranes of the cheeks, and can also appear as vesicles, ulcers, and blisters with a burning sensation. Some patients may develop nail lichen planus, which presents as a thickened, rough, uneven nail plate, or atrophy, with the characteristic presentation of nail pterygium – the disappearance of the nail plate and the nail tubercle covering the nail bed forward. Examination Histopathological manifestations are hyperkeratosis of the epidermis, wedge-shaped thickening of the granular layer, irregular hypertrophy of the spinous layer, liquefied degeneration of the basal cells, and lymphocyte-dominated banding infiltration of the upper dermis. The different subtypes of lichen planus have their own characteristic changes in addition to those described above. Differential diagnosis Lichen planus requires differential diagnosis with the following diseases: dermatodermal amyloidosis, neurodermatitis, psoriasis, annular granuloma, mucocutaneous leukoplakia, and discoid lupus erythematosus of the mouth and lips. Treatment 1. Treatment of chronic lesions, discontinuation of drugs that may trigger the disease. 2. Topical drugs such as strong glucocorticoid ointment, vincristine ointment or calcium-modulated neuronidase inhibitors. 3. Hypertrophic rash can be treated with intra-dermal injection of glucocorticoids. 4. Severe cases may be treated with systemic application of vincristine or glucocorticoids, as well as immunosuppressants. 5. Physical therapy including cryotherapy, laser therapy, narrow-wave ultraviolet therapy are effective. 6. Chinese medicine treatment: Because of the purple-red color of the rash, disc-shaped damage, pigmentation, etc., it has the evidence of Qi stagnation and blood stasis, so it focuses on the treatment of blood circulation and blood stasis. At the same time, we also add drugs to support and benefit Qi such as Chai Hu, Scutellaria baicalensis, Angelica sinensis, Dendrobium, etc.