Fiona M. Lewis Lichen planus (LP) is an inflammatory disorder with manifestations on the skin and genital and oral mucous membranes. The typical features of cutaneous disease were first described by Erasmus Wilson in 1869, but it was not until the 1930s that the link with genital lesions was made by Elizabeth Hunt [1]. It can involve just one of these sites or several in varying combinations, and genital LP can be associated with disease at other sites in up to 68% of cases [2]. It is one of the dermatoses which commonly involves the vulva, and there are several different clinical variants. LP is estimated to affect about 1% of adult females, but the incidence of genital disease is unknown. In patients attending vulval clinics, those with all types of vulval LP varies between 3.7% [3] and 8.8% [4]. The mean age of onset of vulval disease is in the mid‐50s. It is exceptionally rare in children. There is a significant association of the vulvovaginal‐gingival syndrome (VVG) variant of erosive LP with the HLA‐DQB1*0201 allele. This was present in 80% of patients compared with 41.8% of controls [5,6]. It seems, therefore, that patients with vulvovaginal–oral lesions represent a distinct genetic subset. There is now more interest in the genetics of lichenoid variants with different genetic patterns [7]. The pathogenesis of LP is unknown, but it is probably an immunological response by activated T‐cells which target the basal layer of keratinocytes. Weak circulating basement membrane zone antibodies have been shown to be present in 61% of patients with erosive LP of the vulva [8]. There is also a reduction in antioxidant defence and therefore increased oxidative damage in erosive disease [9]. Recent evidence shows more immune changes in vulval LP than in lichen sclerosus (LS) [10]. The gene BIC, which encodes for microRNA‐155 involved in the regulation of the immune system, was increased 17.7‐fold in vulval LP compared with controls. There was also an increase in epidermal FOXP3+ T‐regulatory cells and in dermal CD4+ and CD8+ cells. In a study that included some patients with vulval LP, the NC16A domain of BP180 was a target for circulating T‐cells with associated autoantibodies to BP180 [11]. Although no specific target antigen has been demonstrated in LP, it has been shown that there is disruption of some components of the basement membrane zone, especially hemidesmosomes [12]. It is postulated that this damage may expose epitopes, which can then be a target for an antigen–antibody interaction. LP‐like eruptions can be produced by drugs and are seen in graft‐versus‐host disease (GVHD). It has been suggested that some drugs such as beta blockers and non‐steroidal anti‐inflammatories, but not angiotensin‐converting enzyme inhibitors, may be linked with genital LP [13]. One case of erosive LP involving the vulva is reported after the use of infliximab [14]. Lichenoid reactions can occur on the buccal mucosa adjacent to amalgam restorations, and patients often have positive patch test reactions to relevant allergens, their disease improving when the allergen is withdrawn. However, no similar antigens have been shown for genital disease. There has also been interest in the role of the hepatitis C virus planus as there does seem to be a significant association between hepatitis C infection and LP in southern Europe and Japan, but not in the United Kingdom [15] or northern Europe [16]. Screening for those with vulval LP in these latter populations is therefore unnecessary. Oncogenic human papillomavirus (HPV) types have not been found in erosive LP [17]. The classic histology of LP shows hyperkeratosis in areas of keratinised skin, acanthosis that is typically irregular with a sawtooth appearance, an increased granular layer, and basal cell liquefaction (Figure 24.1). Sometimes there are apoptotic eosinophilic basal and prickle cells, the so‐called colloid bodies. There is a dense, band‐like dermal infiltrate composed mainly of CD8+ T‐cells in close apposition to the dermis. When the basement membrane is disrupted, pigmentary incontinence is common. In the hypertrophic form, the hyperkeratosis and acanthosis are especially marked, but the dermal infiltrate is less evident (Figure 24.2). In erosive LP, the characteristic histological epidermal changes are not always seen, especially if the biopsy is taken from an eroded area. More diagnostic histological features will be seen if the specimen is obtained from the edge of an erosion. In one study that included all types of vulval LP, there was clinical and histological correlation in 75% of cases [18]. Direct immunofluorescence is not routinely done but can help to distinguish immunobullous disease. This reveals staining of the basement membrane zone for fibrinogen and IgM, cytoid bodies, and sometimes granular IgG or IgA in LP. Figure 24.1 Lichen planus – typical histological features with sawtooth rete ridges and dense band‐like infiltrate at dermo‐epidermal junction. Figure 24.2 Hypertrophic lichen planus with marked hyperkeratosis and acanthosis. Just as there is difficulty in distinguishing clinical features from other differential diagnoses, there is also histological difficulty in certain situations. Early LS may be similar to LP histologically, but the presence of cytoid bodies, wedge‐shaped hypergranulosis, basal squamatisation, and pointed rete ridges are features that are much more in favour of LP [19]. Another issue is the regenerative changes at the basement membrane seen in active inflammation, where there may be the presence of mitoses and a reversal of the nucleus‐to‐cytoplasmic ratio. This can be misinterpreted as differentiated vulvar intraepithelial neoplasia (dVIN) and requires expert histopathology input. In this study, copy variant analysis showed an increase in alteration in dVIN but not in erosive LP [20]. The characteristic cutaneous lesions are violaceous, flat papules, which show white streaks over their surface known as Wickham’s striae. These correlate to the hypergranulosis seen histologically. The anogenital lesions of LP may be divided into three main groups according to their clinical presentation: classical, hypertrophic, and erosive (see Table 24.1). There are sometimes overlap features of different types, and in all cases, it is important to examine the rest of the skin and mucous membranes, including the nails, scalp, perianal skin, oral cavity, and lacrimal ducts (Figure 24.3). This type of LP may be asymptomatic, and vulval involvement as part of generalised disease may well be underdiagnosed unless specifically addressed with symptom enquiry and examination. When symptoms do occur, pruritus is the most common complaint. Table 24.1 Main types of lichen planus affecting the vulva. As patients with disease at different sites will present to a variety of specialities, often the focus is only the relevant site for that speciality, and other important issues will not be addressed. For example, dermatologists will usually ask about oral symptoms and will examine the mouth, but genital involvement may be missed, especially if the patient denies any symptoms. Vulval lesions were found in 19 of 37 women presenting with cutaneous LP, with 4 of the 19 being asymptomatic [21]. The incidence of vulval LP in women with oral disease is even higher. In one series of females with oral LP, 57% also had vulval involvement, but half denied any genital symptoms [22]. If a vulval biopsy is done, 87.1% were found to have histological evidence of LP or, in a few cases, LS [23]. In the classical form, the typical lichenoid papules are found on the keratinised anogenital skin (Figure 24.4) and may be associated with Wickham’s striae on the inner aspects of the vulva. This type of LP can exhibit the Koebner phenomenon and arise at sites of minor trauma. After resolution, hyperpigmentation is common, especially in darker skin types. Vaginal lesions do not occur in this type. There can be associated cutaneous, oral, scalp, and nail involvement, and all these sites should be carefully examined. Hypertrophic lesions are the least common type of LP affecting the genital skin. The predominant symptom is severe pruritus. If the lesions ulcerate, then pain can be a common problem. They can be difficult to diagnose as the clinical features of thickened, ulcerated warty plaques are impossible to differentiate clinically from malignancy.
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Lichen Planus
Epidemiology
Genetics
Pathophysiology
Histological features
Clinical features
Classical (papulo‐squamous) LP
Type
Symptoms
Signs
Sites involved
Extra‐genital involvement
Differential diagnosis
Classic (papulo‐squamous)
Pruritus
May be asymptomatic
Papules
Small plaques
Wickham’s striae
Labia majora
Labia minora
Cutaneous
Oral
Scalp
Nails
High‐grade squamous intraepithelial lesion (HSIL)
Warts
Psoriasis
Lupus erythematosus
Hypertrophic
Severe pruritus
Nodules
Labia majora
Perineum
Perianal skin
Cutaneous
Malignancy
Nodular prurigo
Protuberant warts
Lichen simplex
Erosive
Soreness
Dyspareunia/apareunia
Bleeding
Discharge
Difficulty with micturition
Vestibular erosions with lacy edge
Architectural alteration
Vaginal erosions
Vestibule
Inner labia
Vagina
Oral including gingivae
Scalp
Lacrimal ducts
Oesophagus
External auditory meatus
Perianal skin
Mucous membrane pemphigoid
Pemphigus vulgaris
Lichen sclerosus
HSIL
GVHD
Hypertrophic LP
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