Introduction

Numerous pigmented conditions affect the vulva. These include common benign vulvar conditions with a variety of terminology, such as nevus, seborrheic keratosis, acanthosis nigricans (AN), lentigo simplex (lentigines), melanosis, condylomata, pigmented apocrine hamartoma, postinflammatory hyperpigmentation in association with lichen simplex chronicus, vulvar intraepithelial neoplasia (VIN), and angiokeratoma to name a few. Various medical conditions have hyperpigmentation as a sign, such as Cushing's disease, Addison's disease, discoid lupus erythematosus, LAMB syndrome (lentigines, atrial myxomas, mucocutaneous myxomas, and blue nevi) (1), LEOPARD syndrome (lentigines, electrocardiographic-conduction abnormalities, ocular hypertelorism, pulmonary stenosis, abnormal genitalia, retardation of growth, and deafness) (2), Peutz-Jegher (3), and Bannayan-Riley-Ruvalcaba syndrome (4), as well as rarer conditions (5-10). Treatments for medical conditions or trauma can be associated with hyperpigmentation (radiation therapy, chemotherapeutic agents, antimalarials, and metals). While melanoma is the most common malignant process to be associated with hyperpigmentation, other vulvar precancers and cancers may have hyperpigmentation (Paget's disease, squamous cell carcinoma, verrucous carcinoma, and basal cell carcinoma) (11).

The prevalence of pigmented lesions on the vulva was investigated by Rock and Rock in 1990. They performed a yearlong prospective study evaluating pigmented lesions seen in a gynecology practice. Approximately 12% of patients

(37/301) had pigmented lesions or diffuse hyperpigmentation on examination. The majority of patients (84%) were unaware of the pigmentation (12). Many of the common conditions with vulvar pigmentation will be discussed. Management of these various conditions will also be discussed, including careful inspection of the vulva and total body surface, followed by biopsy of any suspicious lesion (13).

MECHANISMS OF HYPERPIGMENTATION

The cause of hyperpigmentation usually is related to the activity and presence of mela-nocytes. Embryologically, the melanocytes are derived from neural crest cells. They migrate into the basal layer of the epidermis. The melanocytes produce melanosomes (organelles that are transferred to keratinocytes). The melanosomes convert tyrosine to melanin, which is responsible for skin color. Various stimuli such as hormones or irritation increase the production of melanosomes resulting in hyperpigmentation (14).

CONDITIONS WITH PIGMENTATION Acanthosis Nigricans

AN is a relatively common skin condition, which tends to occur in skin folds (axillae, under the breasts, and groin) or on the posterior neck. AN may occur on the vulva. It generally presents as a thickened, pigmented, velvety lesion (15). Often it is present on the crural folds. The distribution is often described as a butterfly distribution. It has been found in association with benign and malignant conditions. It may be associated with an underlying medical illness or cancer. There are different forms of AN, but often it is familial. It tends to occur in obese, hirsute, hyperandrogenic women. Grasinger et al. found 24/43 (55.8%) of patients with AN had it present on the vulva (15). AN can be subdivided into the following categories: AN with insulin resistance type A, AN with insulin resistance type B, benign AN, drug-induced AN, hereditary benign AN, malignant AN, and pseudoacanthosis nigricans (16).

Pathophysiology

AN is more common in individuals with darker skin pigmentation. It tends to present at puberty (17). In contrast to the benign form, there is no racial propensity with malignant AN (18). Multiple factors are known to stimulate keratinocytes and dermal fibroblasts to proliferate. The benign and malignant forms have differing pathophysiologies. In the benign form of AN, the stimulation factor is probably insulin or an insulin-like growth factor, which incites epidermal cell propagation. Hyperinsulinemia results in binding of insulin to insulin-like growth factor receptors on the keratinocytes and fibroblasts. This results in hyperplasia of the skin (19). In malignant AN (that is, AN associated with an underlying malignancy), the stimulating factor is hypothesized to be a substance secreted either by the tumor or in response to the tumor. Transforming growth factor is structurally similar to epidermal growth factor and may also be involved in AN. Exogenous medications also have been implicated as etiologic factors (18).

Histopathology

The diagnosis of AN is generally made clinically by the visual appearance, but at times biopsies are indicated. Histologic evaluation in all forms of AN demonstrates hyperkeratosis, papillomatosis, and irregular acanthosis (Fig. 1). Dermal papillae

Achantosis Nigricans Vulvare

Figure 1 Acanthosis nigricans. Lesion demonstrates hyperkeratosis, papillomatosis, and irregular acanthosis.

extend upward in finger-like projections. Horn pseudocysts, as seen in seborrheic keratosis, may be seen. Slight hyperpigmentation of the basal layer of the epidermis is common, but melanocytes are not increased.

Treatment

The treatment of AN must address the underlying cause rather than the appearance of the skin. For example, if insulin resistance is present, it should be managed appropriately. Symptomatic treatments for cutaneous changes include topical antibiotics, topical or systemic retinoids, and keratolytics (20). At times, corticosteroids are utilized. If an underlying endocrinologic abnormality is the cause, the best treatment is weight loss (21) (Table 1).

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