OBSOLETE: Epidermal nevus-vitamin D-resistant rickets syndrome

Epidermal nevus-vitamin D-resistant rickets syndrome, also known as epidermal nevus syndrome with hypophosphatemic rickets, is a rare condition that has been reclassified as obsolete in Orphanet (ORPHA:2694). This syndrome was historically described as the association of widespread epidermal nevi (benign skin growths arising from the epidermis) with hypophosphatemic rickets that is resistant to standard vitamin D therapy. The condition primarily affects the skin and the skeletal system. Patients typically present in childhood with extensive epidermal nevi, often of the keratinocytic or sebaceous type, along with clinical and biochemical features of rickets including bone pain, skeletal deformities (such as bowing of the legs), growth retardation, low serum phosphate levels, and inadequate response to conventional vitamin D supplementation. The underlying mechanism is thought to involve the production of fibroblast growth factor 23 (FGF23) or other phosphaturic factors by the epidermal nevus tissue, leading to renal phosphate wasting and consequent hypophosphatemic rickets. This condition is now generally considered part of the broader spectrum of epidermal nevus syndromes or cutaneous skeletal hypophosphatemia syndrome rather than a distinct entity, which is why the Orphanet entry has been marked as obsolete. Treatment typically involves oral phosphate supplementation combined with active vitamin D analogs (such as calcitriol) to manage the rickets. In some cases, surgical removal or reduction of the epidermal nevus has been reported to improve or resolve the phosphate wasting, supporting the hypothesis that the nevus itself is the source of the phosphaturic substance. Management requires a multidisciplinary approach involving dermatology, endocrinology, and orthopedics.

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