Reticulate Acropigmentation of Kitamura

Reticulate acropigmentation of Kitamura is a rare autosomal dominant disorder with slowly progressive, reticulate brown macules on the dorsum of the hands and feet, with palmar pits and breaks in the dermatoglyphic ridges.

It is mainly reported in Japan, and occurs in other populations. Onset is in the first or second decade. Haploinsufficiency of ADAM10 causes it, and it is allelic with a form of Dowling-Degos disease.

Lesions stay on the hands and feet, and extend to the forearms and legs over years. The condition is benign.

Pathophysiology.

ADAM10 is a metalloprotease involved in Notch signalling. Loss of function alters keratinocyte and melanocyte interaction, leading to epidermal thinning and basal pigmentation.

• Brown reticulate macules with slight atrophy on the backs of the hands and feet, in childhood, which darken with sun exposure.
• Palmar pits and interrupted dermatoglyphs. Freckle like macules on the face in some patients.
• Mild extension to the forearms and legs over decades.

• Clinical diagnosis from distribution and family history.
• Biopsy: hyperpigmented basal layer with thin, elongated rete ridges and no pigment incontinence.
• ADAM10 sequencing for confirmation.

Differential diagnosis.

• Dowling-Degos disease, Dyschromatosis symmetrica hereditaria and Haber syndrome.
• Freckles, xeroderma pigmentosum and pityriasis versicolor.
• Epidermodysplasia verruciformis and acanthosis nigricans.

• Reassure the patient and explain inheritance.
• Sun protection and camouflage cosmetics. Topical tretinoin 0.05% or hydroquinone 4% have limited effect and hydroquinone is used only for short periods.
• Q-switched or fractional lasers can lighten pigment. Results are variable.
• Genetic counselling.

Monitoring. Review every 1 to 2 years.

Referral and escalation. Dermatology; genetics if needed.