15Disorders of Pigmentation on the Vulva
Introduction
Pigmentation can be increased or decreased on the vulva as at other sites. Many lesions that look pigmented on the skin are not always due to increased melanin pigmentation, as vascular lesions and keratinocyte proliferation can also look dark. Increased pigmentation may be diffuse or can occur as discrete lesions. The latter will be discussd separately. Causes of diffuse pigmentation are listed in Table 15.1.
Table 15.1 Causes of diffuse pigmentation.
| Example | |
| Normal variant | Ethnic groups |
| Genetic | Dowling–Degos disease (reticular pigmented anomaly of the flexures) |
| Physiological | Pregnancy |
| Postinflammatory | After lichen planus |
| Post‐traumatic | After obstetric tears |
| Metabolic | Acanthosis nigricans |
| Drug induced | Minocycline |
| Infection | Tinea, erythrasma |
| Malignancy | Acanthosis nigricans |
| Idiopathic | Vulval melanosis |
Diffuse pigmentation can occur in those with darker skin types as a variation of normal. In pregnancy, there is increased melanogenesis, which gives rise to facial chloasma, the linea nigra on the abdomen (Figure 15.1) and can also cause darkening of the vulva.
Figure 15.1 Linea nigra.
Postinflammatory Pigmentation
A degree of hyperpigmentation is common after almost any inflammatory process on the vulva (Figure 15.2) but it most commonly occurs after lichen planus and a fixed drug eruption. It usually fades but may take many months to do so, particularly in darker skinned individuals. The histology shows pigment incontinence and pigmented macrophages in the dermis.
Figure 15.2 Postinflammatory hyperpigmentation after eczema.
Post‐Traumatic Pigmentation
Trauma is sometimes followed by pigmentation. Obstetric and surgical scars may pigment and this often resolves with time.
Acanthosis Nigricans
Acanthosis nigricans is thought to be caused by factors that increase the proliferation of keratinocytes and dermal fibroblasts. Different types of acanthosis nigricans are given in Table 15.2. There is a strong link with hyperinsulinaemia and insulin. Insulin‐like growth factors are thought to be the causative factor. There is also an association with malignancy in some cases and substances secreted by the tumour cause the epidermal growth in these patients. The clinical features of the benign and malignant forms are identical. Sweating, moisture and friction are also factors as acanthosis nigricans has a predilection for body folds such as the neck, axillae (Figure 15.3) and inguinal folds.
Table 15.2 Types of acanthosis nigricans.
| Obesity associated | |
| Endocrine syndromes | Acromegaly |
| Familial | Autosomal dominant, usually starts in childhood |
| Drug induced | Nicotinic acid, insulin, steroids |
| Malignancy |
Figure 15.3 Acanthosis nigricans in axilla.
It is estimated that over half of patients who are overweight have a degree of acanthosis nigricans. The malignant form is rare and is often diagnosed at the same time as the malignancy. However, it may occur prior to this diagnosis and in older patients who are not obese with sudden onset of the skin disease; it is important to take a full history and investigate further if necessary. The most commonly associated malignancies are adenocarcinomas of the gastrointestinal tract, especially the stomach (approximately 55% of cases of malignant acanthosis nigricans).
The lesions are thickened and darkened and as they increase in size they form plaques with a velvet surface (Figure 15.4). Skin tags are frequently found on the surface. The inguinal folds and outer labia majora are common sites along with other flexures. The areolae may be involved. The lesions are asymptomatic but the patients may be very troubled by the cosmetic appearance.
Figure 15.4 Thickened velvety surface seen in acanthosis nigricans.
There is hyperkeratosis and marked papillomatosis. The darkening of the skin seen clinically is due to the hyperkeratosis. There is no increase in the number of melanocytes or melanin production.
Management
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