10 Psoriasis is one of the most common skin diseases and is due to an abnormal proliferation of the epidermis resulting in the characteristic scaly, erythematous plaque. Vulval psoriasis is a common diagnosis in the vulval clinic and studies suggest that psoriasis may account for 5% of those presenting with vulval symptoms. At this site, it is sometimes referred to as flexural, inverse or intertriginous psoriasis. The worldwide prevalence of psoriasis is estimated at 2%. Vulval psoriasis may be found in up to 65% of patients with psoriasis elsewhere but patients are often embarrassed about the disease in the genital area and may not volunteer to describe symptoms at this site unless specifically asked. Vulval psoriasis can occur in isolation, without any obvious disease at other sites. The pathophysiology of genital psoriasis is the same as that elsewhere. There is activation of T lymphocytes leading to an abnormal and accelerated proliferation of keratinocytes. The renewal of the epidermis is reduced from the normal 30 days to about 7 days. The Koebner phenomenon describes the occurrence of skin disease at sites of trauma such as in surgical scars or other areas of injury. Psoriasis is one of the skin diseases that exhibits this frequently and it is postulated that friction, moisture and irritant effects in the flexures may contribute to the development of psoriasis at these sites. Certain drugs can exacerbate psoriasis and a full drug history is very helpful. Beta blockers, lithium carbonate and chloroquine are known to make psoriasis worse in some patients. Genetic factors are also involved in the development of psoriasis. Stress and infection are known to be triggers for the onset of disease in predisposed patients. The classic psoriasiform histology includes regular acanthosis of the epidermis, some spongiosis and elongation of the epidermal ridges and dermal papillae. Intraepidermal neutrophils are seen singly or more typically as small collections. Mitotic activity is marked due to the increased proliferation seen in the condition. Not only are the clinical features of psoriasis lost in flexural disease but the histological pattern is not always characteristic. Spongiosis can be a predominant feature and the histological appearances can be difficult to distinguish from eczema. The most commonly reported symptom of vulval psoriasis is pruritus. Patients often report that this is worse at night and there may be a premenstrual exacerbation. If the lesions fissure, then soreness, discomfort and minor bleeding may occur. These fissures can be very painful and superficial dyspareunia is common. It can have a significant impact on quality of life and sexual function. The classical psoriatic lesion is the scaly erythematous plaque (Figure 10.1). The scaling is silvery in superficial lesions but hyperkeratosis can occur with thickened crusty areas. The classic sites involved are the extensor surfaces (elbows and knees), scalp and ears (Figure 10.2). More widespread involvement affects the trunk and limbs. The face is usually spared. Typical changes occur in the nails with thimble pitting, onycholysis (where the nail plate separates from the nail bed) and hyperkeratosis under the nail plate (Figure 10.3). About 10% of patients will have an associated arthropathy. Figure 10.1 Typical psoriatic plaque on elbow showing silver scales.
Psoriasis
Introduction
Incidence
Pathophysiology
Histological features
Symptoms
Clinical features
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