Flexural Reticulate Hyperpigmentation Unmasking Dowling-Degos Disease: A Clinical and Histopathological Insight

Abstract

Dowling–Degos disease (DDD) is a rare inherited genodermatosis characterised by progressively developing reticulate hyperpigmentation, most commonly in flexural areas. Its clinical appearance can resemble other pigmentary disorders, making clinicopathological assessment important. We describe a 40-year-old woman with a two-year history of gradually extending lentiginous hyperpigmented macules. The lesions initially involved the axillae and submammary folds and subsequently affected the neck and genital region. She reported no similar family presentation, and no systemic symptoms, metabolic abnormalities or associated cutaneous findings were identified. Dermoscopy revealed a fine reticulate pigmented network and seborrhoeic keratosis-like features. Histopathological examination demonstrated elongated rete ridges, increased pigmentation of the basal epidermal layer and keratin-filled horn cysts, supporting a diagnosis of DDD. Genetic testing was unavailable; therefore, a molecular subtype could not be established. The distribution and morphology of the lesions, together with the dermoscopic and histopathological findings, were considered in differentiating DDD from acanthosis nigricans, lentiginosis syndromes and other reticulate pigmentary disorders. The patient did not seek treatment for the skin condition. Available management approaches are largely symptomatic and directed towards cosmetic concerns, with variable responses reported for topical and laser-based treatments. This case illustrates the value of integrating clinical examination, dermoscopy and histopathology when genetic confirmation is unavailable, while recognising the limitations of a single case in informing treatment decisions.