Idiopathic guttate hypomelanosis

Definition

Idiopathic guttate hypomelanosis is a common, benign, acquired leukoderma with small, well-defined, porcelain-white macules on sun-exposed limbs.

Occurrence & epidemiology

Both sexes and all skin types are affected. It mostly affects people over 40 years, and its frequency rises with age – up to about 90% in the ninth decade. It is uncommon in children and teenagers; familial cases are common.

Aetiopathogenesis

Probably multifactorial: skin ageing, chronic UV exposure, genetic factors, trauma and autoimmunity. Abnormal uptake of melanin by keratinocytes has been demonstrated, reducing pigment transfer from melanocytes.

Clinical features

• Smooth, hypo- or depigmented, round to oval macules of 2–5 mm (up to 1.5 cm), usually multiple and asymptomatic.
• Mainly on the extensor forearms, the shins and the V of the chest.
• More obvious in skin of colour.
• Variants: hypopigmented macules on sun-damaged skin; a single white stellate sclerotic macule; small macules with a scalloped margin and hyperkeratotic surface.

Histology

Flattened, thin epidermis with basket-weave hyperkeratosis and loss of rete ridges; melanin in the epidermis reduced or absent; melanocytes normal or reduced, with short retracted dendrites; small foci of retained melanin in the basal layer.

Diagnosis

• Usually a clinical diagnosis.
• Wood lamp emphasises the loss of pigment.
• Dermoscopy: well-defined white structureless areas, absent pigment network.
• Biopsy only to exclude other leukodermas, such as vitiligo or lichen sclerosus.

Differential diagnoses

• Vitiligo
• Pityriasis alba
• Naevus depigmentosus (achromic naevus)
• Lichen sclerosus
• Pityriasis versicolor (tinea versicolor)

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References (selection)

1. DermNet: Idiopathic guttate hypomelanosis
2. Idiopathic Guttate Hypomelanosis: A Review of its Etiology, Pathogenesis, Findings, and Treatments

Cross-references