Phakomatosis pigmentokeratotica

Phakomatosis pigmentokeratotica (PPK) is an extremely rare congenital skin disorder classified among the epidermal nevus syndromes. It is characterized by the coexistence of two distinct types of skin lesions: an organoid or sebaceous nevus (nevus sebaceus of Jadassohn), typically arranged in a linear or blaschkoid pattern, and a speckled lentiginous nevus (nevus spilus-type macular lesion) that is often widespread. These two nevi are thought to arise from a twin-spot phenomenon involving postzygotic somatic mutations, specifically activating mutations in HRAS and KRAS genes in a mosaic pattern. The condition affects multiple body systems beyond the skin. Neurological involvement may include intellectual disability, seizures, and cranial nerve abnormalities. Skeletal abnormalities such as hypophosphatemic rickets (vitamin D-resistant rickets), scoliosis, and limb asymmetry have been reported. Some patients develop excessive sweating (hyperhidrosis) on the affected side. Additional features can include ocular abnormalities, ptosis, and rarely, malignant transformation of the sebaceous nevus component into basal cell carcinoma or other tumors. There is no curative treatment for phakomatosis pigmentokeratotica. Management is multidisciplinary and symptom-based. Dermatological surveillance is important due to the risk of secondary neoplasms arising within the nevi. Hypophosphatemic rickets, when present, requires phosphate supplementation and active vitamin D analogs. Surgical excision of the sebaceous nevus may be considered for cosmetic reasons or if malignant transformation is suspected. Neurological and orthopedic complications are managed according to standard clinical protocols. Regular follow-up with dermatology, endocrinology, neurology, and orthopedics is recommended depending on the individual's clinical manifestations.

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