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SynopsisPhakomatosis pigmentokeratotica (PPK) is a subtype of epidermal nevus syndrome, in which a nevus sebaceus and one or more speckled lentiginous nevi occur simultaneously. It is an extremely rare syndrome, with only about 30 cases reported in the literature. It is more commonly seen in males, with a 2.4:1 male to female predominance. Activating postzygotic mutations in HRAS are thought to be responsible for PPK.
Typically, the nevus sebaceus has a blaschkoid distribution and the speckled lentiginous nevi are segmental, sometimes with the appearance of a checkerboard pattern. While the nevus sebaceus is usually present at birth, the speckled lentiginous nevi may be identified in the first 2 years of life or later. As is the case within nonsyndromic nevi sebaceus, a range of benign neoplasms and basal cell carcinoma may develop. Cases of melanoma developing within the speckled lentiginous nevi have also been reported.
PPK can be associated with neurological, musculoskeletal, and ophthalmological findings in up to two-thirds of patients. Among these, neurological findings are the most common and include hemiparesis, hyperhidrosis, dysesthesia, hyperpathia, intellectual disability, seizures, and other sensory and/or motor neuropathies. Musculoskeletal findings can include hemiatrophy, scoliosis, kyphosis, hypophosphatemic vitamin D-resistant rickets, and muscular weakness. Reported ophthalmological findings include strabismus, ptosis, congenital glaucoma, coloboma, and esotropia. Other clinical features include facial dysmorphism, conductive hearing loss, and aortic and renal artery stenosis. Abdominal wall and vaginal rhabdomyosarcoma, nephroblastoma (Wilms tumor), and pheochromocytoma have been reported.
Q85.8 – Other phakomatoses, not elsewhere classified
723455009 – Phakomatosis pigmentokeratotica
Differential Diagnosis & Pitfalls
- Schimmelpenning-Feuerstein-Mims syndrome is another organoid nevus syndrome. It can have the same heterozygous mosaic HRAS and KRAS mutations; however, the mutated progenitor cells only have the ability of differentiating into epithelial cells and thus will only have the epidermal nevus.
- Phakomatosis pigmentovascularis
- Proteus syndrome
- Congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD) syndrome
- Nevus comedonicus syndrome
- Becker nevus syndrome
- Noonan syndrome is a germline mosaicism but can also have vaginal rhabdomyosarcoma.
- Angora hair nevus syndrome