Idiopathic guttate hypomelanosis

Introduction

Idiopathic guttate hypomelanosis (IGH) is a very common acquired, benign leukoderma of unknown etiology. IGH is most commonly a complaint of middle-aged, light-skinned women, but it is increasingly seen in both sexes and older dark-skinned people with a history of long-term sun exposure. 

 

Pathology

The most consistent histologic features of IGH are a basket‐weave hyperkeratosis with epidermal atrophy and flattening of the dermal–epidermal junction, with moderate to marked reduction or focal absence of melanin granules in the basal and suprabasal layers. There is a moderate to marked reduction in the number of DOPA-positive epidermal melanocytes (10–50% compared with normal skin), but these cells are never totally absent.

IGH has been hypothesized to be UV induced. Some suggest that IGH results from age related somatic mutation of melanocytes.

 

Clinical features

The typical IGH lesion is a circumscribed, asymptomatic porcelain white macule. The lesions are usually 2–5 mm in diameter but sometimes much larger up to 2.5 cm in size. Once present, they do not change in size or coalesce. The border is sharply defined, often angular and irregular; their surface is smooth and the skin markings are normal. Spontaneous repigmentation has not been reported. Hairs within the lesions usually retain their pigment.  Lesions are multiple and most commonly located on the extensor surface of the forearms and shins; the remainder of the extremities can be affected, but rarely the face. Non‐actinic lesions occur in dark skinned people and may be located in unexposed areas such as on the trunk.

 

Treatment

Treatment is not usually required. Cryotherapy with liquid nitrogen for 3 to 5 seconds has been described as a possible therapy for IGH. As sunlight is most likely a precipitating factor, use of sunscreens and physical barriers should be recommended.

Treatment with topical tretinoin for 4 months restores the elasticity, with a partial restoration of pigmentation. A variety of other therapies have been advocated for IGH, including topical steroids, topical tacrolimus and superficial dermabrasion. None are predictably successful.