13 Lichen planus (LP) is another dermatosis that specifically affects the vulva but, unlike lichen sclerosus, it can affect many other cutaneous and mucosal sites and has a wide variety of clinical types and presentations. Lichen planus is slightly more common in females (approximately 55% of cases) than males and most commonly starts in the 40s and 50s. Vulval LP is rare in children. The incidence of vulval LP is unknown. In one series of 3350 women seen in a vulval clinic, 3.7% had LP on histology and the erosive type of LP was seen in 17.6% of these. Most patients who are diagnosed with cutaneous LP will be asked about, and examined for, oral disease but this is often not the case for genital lesions. Over half of women who present with cutaneous LP have vulval involvement with the disease but may be asymptomatic and so, if not specifically examined, this group may be missed. It is likely that LP is a T‐lymphocyte‐mediated inflammatory disorder but specific antigens have not been identified. On the oral mucosa, lichenoid reactions are seen adjacent to metal amalgam fillings, which resolve if the filling is removed, suggesting an antigen‐antibody interaction. The lichenoid form of graft versus host disease has features that are indistinguishable from those of LP on the mucosa. A link between LP and hepatitis C infection has been demonstrated in some populations in southern Europe but not in others and there is no link in northern Europe. An association with other autoimmune diseases such as thyroid disease, pernicious anaemia, vitiligo and alopecia areata can be seen in patients with LP. A genetic link has been demonstrated with the vulvo‐vaginal‐gingival subtype of erosive LP. The typical features of LP are a thickened epidermis with a prominent granular cell layer and irregular ‘saw‐tooth’ acanthosis. Under the basal layer, a dense dermal inflammatory infiltrate consisting mainly of T lymphocytes occurs in a bandlike pattern (Figure 13.1). Basal cell liquefactive degeneration with the formation of colloid bodies (apoptotic basal cells) is typical. Pigmentary incontinence is common. Some atypia can occur in the basal layer as the cells regenerate and it is important not to mistake this for intraepithelial neoplasia. Figure 13.1 Typical histological features of LP. These classical features are most likely to be evident in classic and hypertrophic LP. The appearances may be altered on mucosal surfaces and this is a particular issue with erosive LP where the epidermis is lost and the pathologist may report a nonspecific inflammation related to the dense inflammatory cell infiltrate. The best area to take the biopsy if erosive LP is suspected is across the edge of an erosion. Plasma cells may be frequent in genital, LP especially if the biopsy is taken from the vestibule. The classic lesions of LP are violaceous papules with a white network on the surface, known as Wickham’s striae (Figure 13.2). The cutaneous lesions are typically found on the flexor aspects of the wrists, lower limbs and trunk. Flexural lesions affecting the axillae, inframammary areas and inguinal folds can occur with or without lesions elsewhere. The lesions can be very itchy and typically leave significant postinflammatory hyperpigmentation as they resolve, especially in the flexures (Figure 13.3). Figure 13.2 Plaque of lichen planus with Wickham’s striae on the surface. Figure 13.3 Postinflammatory hyperpigmentation in inguinal fold. Scarring alopecia may be patchy, generalized or in a specific frontal pattern known as frontal fibrosing alopecia or Kossard’s disease. A destructive nail dystrophy is seen in some patients.
Lichen Planus
Introduction
Epidemiology
Incidence
Pathophysiology
Histological Features
Clinical Features of Lichen Planus
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