Phacomatosis pigmentokeratotica: a 20-year follow-up with malignant degeneration of both nevus components

Phacomatosis spilosebacea: A new name for a distinctive binary genodermatosis

Phacomatosis pigmentokeratotica (PPK) is defined by the association of papular nevus spilus arranged in a flag-like pattern and sebaceous nevus following Blaschko's lines. A systematic search of the worldwide literature retrieved 95 well-established PPK cases. An additional 30 cases were excluded for a number of reasons. Based on this study, we propose to rename PPK phacomatosis spilosebacea (PSS). Mosaic mutations of the HRAS gene are the only proven cause of PSS. The extracutaneous abnormalities of PSS result from various degrees of intermingling of Schimmelpenning syndrome and papular nevus spilus syndrome. PSS seems to be a condition at particularly high risk of developing basal cell carcinoma, urogenital malignancies, and vitamin D-resistant hypophosphatemic rickets. Extracutaneous abnormalities were detected in approximately 75% of PSS cases.

Optical coherence tomography confirms non-malignant pigmented lesions in phacomatosis pigmentokeratotica using a support vector machine learning algorithm

INTRODUCTION

Phacomatosis pigmentokeratotica (PPK), an epidermal nevus syndrome, is characterized by the coexistence of nevus spilus and nevus sebaceus. Within the nevus spilus, an extensive range of atypical nevi of different morphologies may manifest. Pigmented lesions may fulfill the ABCDE criteria for melanoma, which may prompt a physician to perform a full-thickness biopsy.

MOTIVATION

Excisions result in pain, mental distress, and physical disfigurement. For patients with a significant number of nevi with morphologic atypia, it may not be physically feasible to biopsy a large number of lesions. Optical coherence tomography (OCT) is a non-invasive imaging modality that may be used to visualize non-melanoma and melanoma skin cancers.

MATERIALS AND METHOD

In this study, we used OCT to image pigmented lesions with morphologic atypia in a patient with PPK and assessed their quantitative optical properties compared to OCT cases of melanoma. We implement a support vector machine learning algorithm with Gabor wavelet transformation algorithm during post-image processing to extract optical properties and calculate attenuation coefficients.

RESULTS

The algorithm was trained and tested to extract and classify textural data.

CONCLUSION

We conclude that implementing this post-imaging machine learning algorithm to OCT images of pigmented lesions in PPK has been able to successfully confirm benign optical properties. Additionally, we identified remarkable differences in attenuation coefficient values and tissue optical characteristics, further defining separating benign features of pigmented lesions in PPK from malignant features.

Noninvasive imaging exploration of phacomatosis pigmentokeratotica using high-frequency ultrasound and optical coherence tomography: Can biopsy of PPK patients be avoided?

BACKGROUND

Phacomatosis pigmentokeratotica (PPK) is a distinct and rare type of epidermal nevus syndrome characterized by coexisting nonepidermolytic organoid sebaceous nevus (SN) with one or more speckled lentiginous nevi (SLN). Atypical nevi including compound Spitz and compound dysplastic may manifest within regions of SLN. Patients with PPK, or similar atypical nevus syndromes, may be subject to a significant lifetime number of biopsies, leading to pain, scarring, anxiety, financial burden, and decreased quality of life. The current literature includes case reports, genetics, and associated extracutaneous symptoms of PPK, but use of noninvasive imaging techniques have not been explored. We aim to investigate the value of high-frequency ultrasound (HFUS) and optical coherence tomography (OCT) in discriminating morphological features of pigmented lesions and nevus sebaceous within one patient with PPK.

MATERIALS AND METHODS

Two modalities, (1) HFUS imaging, based on acoustic properties and (2) OCT imaging, based on optical properties, were used to image a patient with PPK. Benign pigmented lesions, which may raise clinical suspicion for significant atypia, and nevus sebaceous, were selected on different areas of the body to be studied.

RESULTS

Five pigmented lesions and one area of nevus sebaceous were imaged and analyzed for noninvasive features. Distinct patterns of hypoechoic features were seen on HFUS and OCT.

CONCLUSION

HFUS provides a deep view of the tissue, with ability to differentiate gross structures beneath the skin. OCT provides a smaller penetration depth and a higher resolution. We have described noninvasive features of atypical nevi and nevus sebaceous on HFUS and OCT, which indicate benign etiology.

Phacomatosis Pigmentokeratotica: A Mosaic RASopathy with Malignant Potential

Phacomatosis pigmentokeratotica (PPK) is a rare epidermal nevus syndrome characterized by the co-occurrence of a nevus sebaceous arranged along the lines of Blaschko with a speckled lentiginous nevus (SLN). We report a novel KRAS mutation in a patient with a large nevus sebaceous and an SLN who subsequently developed a vaginal botryoid rhabdomyosarcoma, an association not previously reported in the literature. This case expands our knowledge of the genetic basis for phacomatosis, in which mutations in HRAS have been previously described, although this report provides evidence that activating mutations in KRAS or HRAS may cause PPK. This report confirms that PPK is a mosaic RASopathy with malignant potential and raises the question of whether screening for other RAS-associated malignancies should be performed for all children with PPK.

Combined melanocytic and sweat gland neoplasm: cell subsets harbor an identical HRAS mutation in phacomatosis pigmentokeratotica

Phacomatosis pigmentokeratotica (PPK) is characterized by the co-existence of epidermal nevi and large segmental speckled lentiginous nevi of the papulosa type. PPK, previously explained as 'twin spot' mosaicism due to the postzygotic crossing-over of two homozygous recessive mutations, has recently been shown to derive from one postzygotic activating RAS mutation. Epidermal nevi, including those in PPK, are known to give rise to neoplasms such as trichoblastoma and basal cell carcinoma. Within speckled lentiginous nevi, Spitz nevi and melanoma have been well documented. We report a case of PPK with a combined melanocytic and adnexal neoplasm presenting where the nevi conjoined. Using next-generation sequencing techniques, we were able to identify the same HRAS G13R mutation within both components of the tumor, and to show the absence of additional mutated modifier genes in a panel of 300 cancer-related genes. Given the genetic findings in this rare tumor-type, we suggest that this case may be used as a model for understanding the development of biphenotypic neoplasia or intratumoral heterogeneity in some cases.

Phacomatosis pigmentokeratotica is a "pseudodidymosis"

In phacomatosis pigmentokeratotica, papular nevus spilus coexists with nevus sebaceus. The disorder was thought to be a didymosis with early postzygotic recombination. In this issue, however, Groesser and co-workers provide a new concept. Both nevi originate from a single heterozygous HRAS mutation in a pluripotent progenitor cell. This new understanding has implications for other proposed examples of didymosis in humans.

Phacomatosis pigmentokeratotica without extracutaneous abnormalities: a case study involving a preterm baby

Phacomatosis pigmentokeratotica (PPK) is a rare syndrome defined by the association of an organoid nevus occasionally with sebaceous differentiation, a speckled lentiginous nevus, and other extracutaneous anomalies. A preterm male infant of only 830 g at 27 week gestational age had an organoid nevus showing sebaceous differentiation. Also, he had multiple speckled-lentiginous nevus. Correlating the observed clinical presentation with the histopathological findings, the diagnosis of PPK was established. There have been less than 10 cases of PPK without extracutaneous manifestation. We present an uncommon case of a preterm patient with PPK who had no extracutaneous abnormalities.

Phacomatosis pigmentokeratotica: a further case without extracutaneous anomalies and review of the condition

Epidermal nevus syndrome is the term for the association of an epidermal nevus and extracutaneous anomalies, including neurologic, ophthalmic, and skeletal defects. Epidermal nevus syndromes include different disorders that share the feature of mosaicism. Phacomatosis pigmentokeratotica (PPK) is a distinctive new epidermal nevus syndrome first described in 1996 characterized by the presence of multiple organoid nevi with sebaceous differentiation, a speckled lentiginous nevus, and skeletal and neurologic abnormalities. Only a handful of cases of PPK without extracutaneous manifestations have been reported. We report here an individual with PPK with only cutaneous signs and confirm this distinctive syndrome has two subtypes according to the presence or absence of extracutaneous involvement.

Epidermal nevi

Nevi or nests of cells may be made up of a variety of cell types. The cell types that live in the epidermis include epidermal cells or keratinocytes, sebaceous glands, hair follicles, apocrine and eccrine glands, and smooth muscle cells. This article discusses epidermal or keratinocyte nevi, nevus sebaceous, nevus comedonicus, smooth muscle hamartomas, and inflammatory linear verrucous epidermal nevi. Syndromes associated with epidermal nevi are also reviewed.

The group of epidermal nevus syndromes Part I. Well defined phenotypes

The epidermal nevus syndromes represent a group of distinct disorders that can be distinguished by the type of associated epidermal nevus and by the criterion of presence or absence of heritability. Well defined syndromes characterized by organoid epidermal nevi include Schimmelpenning syndrome, phacomatosis pigmentokeratotica, nevus comedonicus syndrome, angora hair nevus syndrome, and Becker nevus syndrome. The molecular basis of these disorders has so far not been identified. By contrast, the group of syndromes characterized by keratinocytic nevi comprises three phenotypes with a known molecular etiology in the form of CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, type 2 segmental Cowden disease, and fibroblast growth factor receptor 3 epidermal nevus syndrome (García-Hafner-Happle syndrome), whereas Proteus syndrome is still of unknown origin. From this overview, it is clear that a specific type of these disorders cannot be classified by the name "epidermal nevus syndrome" nor by the terms "organoid nevus syndrome" or "keratinocytic nevus syndrome."

LEARNING OBJECTIVES

After completing this learning activity, participants should be able to distinguish nine different epidermal nevus syndromes by their characteristic features, understand the practical significance of avoiding terms like "epidermal nevus syndrome" or "keratinocytic nevus syndrome" to define any specific entity within this group of disorders, and differentiate between nonhereditary traits and those bearing a genetic risk because of either Mendelian or non-Mendelian inheritance.

Carcinomas basocelulares múltiples sobre facomatosis pigmentoqueratótica

We present a patient with phacomatosis pigmentokeratotica (PPK) who developed several basal cell carcinomas on epidermal nevus lesions in adult life. PPK shows an elevated incidence of development of malignant lesions both on the sebaceous or epidermal nevus component as well as on the nevus spilus one.

Phacomatosis pigmentokeratotica associated with hemihypertrophy and a rhabdomyosarcoma of the abdominal wall

Phacomatosis pigmentokeratotica (PPK) represents a specific "twin nevus" syndrome in which a speckled lentiginous nevus (SLN) is associated with an organoid nevus with sebaceous differentiation. A boy with a large nevus sebaceus on the left face and upper part of the trunk, a giant segmental SLN extending from the abdomen to the feet bilaterally, and right hemihypertrophy developed an embryonal rhabdomyosarcoma of the right abdominal wall at age 6 months. A variety of musculoskeletal, neurologic, and ocular anomalies have been observed in patients with PPK, reflecting the individual manifestations of both SLN and Schimmelpenning syndromes. This report adds hemihypertrophy to the spectrum of extracutaneous manifestations of PPK and, to our knowledge, represents the first observation of a rhabdomyosarcoma arising in contiguity with an SLN in a patient with PPK. The development of a rhabdomyosarcoma in our patient likely reflects both increased propensity for growth (as evidenced by the hemihypertrophy) and the pluripotent nature of neural-crest derived cells within the field defect that underlies an SLN.