Epidermal nevus syndromes

Multiple adenomatoid odontogenic tumors in a patient with Schimmelpenning syndrome

Schimmelpenning syndrome (SS) is a congenital neurocutaneous disorder characterized by the presence of linear nevus sebaceous, ophthalmic, neurologic, skeletal, urologic, and cardiovascular alterations. Oral manifestations related to SS mainly include dental defects, papillary lesions in the oral mucosa, giant cell lesions of the jaws, and odontogenic tumors. Here, we report the first case of multiple adenomatoid odontogenic tumor observed in a patient with SS.

Epidermal nevus syndromes

The term epidermal nevus syndrome (ENS) has been used to describe the association of epidermal hamartomas and extracutaneous abnormalities. Although many continue to use the term "ENS," it is now understood that this is not one disease, but rather a heterogeneous group with distinct genetic profiles defined by a common cutaneous phenotype: the presence of epidermal and adnexal hamartomas that are associated with other organ system involvement. One commonality is that epidermal nevi often follow the lines of Blaschko and it appears the more widespread the cutaneous manifestations, the greater the risk for extracutaneous manifestations. The majority of the extracutaneous manifestations involve the brain, eye, and skeletal systems. The CNS involvement is wide ranging and involves both clinical manifestations such as intellectual disability and seizures, as well as structural anomalies. Several subsets of ENS with characteristic features have been delineated including the nevus sebaceus syndrome, Proteus syndrome, CHILD syndrome, Becker's nevus syndrome, nevus comedonicus syndrome, and phakomatosis pigmentokeratotica. Advances in molecular biology have revealed that the manifestations of ENS are due to genomic mosaicism. It is likely that the varied clinical manifestations of ENS are due in great part to the functional effects of specific genetic defects. Optimal management of the patient with ENS involves an interdisciplinary approach given the potential for multisystem involvement. Of note, epidermal nevi have been associated with both benign and malignant neoplasms, and thus ongoing clinical follow-up is required.

Mosaic RASopathies

"RASopathies" are a group of developmental syndromes with partly overlapping clinical symptoms that are caused by germline mutations of genes within the Ras/MAPK signaling pathway. Mutations affecting this pathway can also occur in a mosaic state, resulting in congenital syndromes often distinct from those generated by the corresponding germline mutations. For syndromes caused by mosaic mutations of the Ras/MAPK signaling pathway, the term "mosaic RASopathies" has been proposed. In the following article, genetic and phenotypic aspects of mosaic RASopathies will be discussed.

Hemimegalencephalic variant of epidermal nevus syndrome: case report and literature review

The epidermal nevus syndrome (ENS) is an uncommon neurocutaneous disorder in which epidermal nevi are found in association with congenital abnormalities of the brain, eye, and/or skeleton. The association of epidermal nevi and neurologic abnormalities was comprehensively described by Schimmelpenning in 1957. Pavone et al. (1991) identified a homogeneous variant of ENS with hemimegalencephaly, gyral malformation, mental retardation, seizures and facial hemihypertrophy. A 13-year-old boy with the neurologic variant of ENS with hemimegalencephaly, facial asymmetry, febrile seizures and mental retardation is reported. Additionally, we performed a literature review using the search terms "epidermal nevus syndrome" and "hemimegalencephaly", including secondary sources of data such as reference lists of articles reviewed. We found 57 previously reported cases with the hemimegalencephalic variant of epidermal nevus syndrome, in which the most frequent associated features are severe epilepsy, in about half of cases with neonatal onset, mental retardation/developmental delay, ocular/visual involvement, and facial abnormalities.

Hybrid follicular cyst (pilomatrical and infundibular) arising within a sebaceous nevus

A 7-year-old girl presented with a 3-month history of a small blue-brown papule arising within a large sebaceous nevus on her temporal scalp. A punch excision was performed that demonstrated a hybrid follicular cyst. The majority of the cyst wall displayed pilomatrical differentiation consisting of basaloid matrical-type cells with luminal shadow cell keratinization. The matrical epithelium displayed strong membranous, cytoplasmic, and nuclear staining for β-catenin. Only a small component of the wall displayed infundibular differentiation. These findings were consistent with a hybrid follicular cyst predominantly displaying pilomatrical differentiation with only a small component of infundibular lining. The most common tumors arising within sebaceous nevi are the syringocystadenoma papilliferum and trichoblastoma. Follicular cysts with infundibular (sebaceous cyst) and trichilemmal (pilar cyst) differentiation are exceedingly common, although their development within sebaceous nevi appears to be rare. We report a rare case of a hybrid follicular cyst with matrical differentiation occurring within a sebaceous nevus.

Systemic epidermal nevus with involvement of the oral mucosa due to FGFR3 mutation

BACKGROUND

Epidermal nevi (EN) represent benign congenital skin lesions following the lines of Blaschko. They result from genetic mosaicism, and activating FGFR3 and PIK3CA mutations have been implicated.

CASE PRESENTATION

We report a female patient with a systemic keratinocytic nevus also involving the oral mucosa. Molecular genetic analysis revealed a mosaicism of the FGFR3 hotspot mutation R248C in the EN lesions of the skin and of the oral mucosa. The detection of the R248C mutation in a proportion of blood leukocytes and a slight scoliosis suggest an EN syndrome.

CONCLUSIONS

Our results show that activating FGFR3 mutations can also affect the oral mucosa and that extracutaneous manifestations of EN syndrome can be subtle. We highlight the theoretical risk of the patient having an offspring with thanatophoric dysplasia as gonadal mosaicism for the R248C mutation cannot be excluded.

The group of epidermal nevus syndromes Part II. Less well defined phenotypes

In addition to the well established epidermal nevus syndromes, such as Schimmelpenning, Becker, Proteus, CHILD, or nevus comedonicus syndromes, the group of less well defined phenotypes associated with epidermal nevi presently includes nevus trichilemmocysticus syndrome, didymosis aplasticosebacea, SCALP syndrome (sebaceous nevus, central nervous system malformations, aplasia cutis congenita, limbal dermoid,and pigmented nevus), Gobello syndrome, Bäfverstedt syndrome, NEVADA syndrome (nevus epidermicus verrucosus with angio-dysplasia and aneurysms), and CLOVE syndrome (congenital lipomatous overgrowth, vascular malformations, and epidermal nevus). These syndromes can thus far be regarded as being in limbo. Future clinical and molecular research may show which of these disorders can be added to the list of well defined nosologic entities.

LEARNING OBJECTIVES

After completing this learning activity, participants should be able to understand why the list of distinct epidermal nevus syndromes can thus far not be regarded as being complete; why clinicians, when seeing a patient with an epidermal nevus syndrome that is difficult to categorize, should bear in mind the group of less well defined epidermal nevus syndromes; and how practical dermatologists can help recognize rare forms of epidermal nevus syndromes and categorize them appropriately.

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.

An epidermal nevus syndrome with cerebral involvement caused by a mosaic FGFR3 mutation

A 5-year-old Mexican girl had a bilateral, systematized epidermal nevus of a non-epidermolytic, non-organoid type covering large parts of her body with the exception of the scalp. Clinically, this nevus was of a soft, velvety type showing affinity to the large body folds. Histopathological examination revealed orthohyperkeratosis and papillomatosis without granular degeneration and without any abnormality of adnexal structures. During infancy she developed seizures, and subsequently a delayed mental development was noted. Computer tomography of the brain revealed cortical and subcortical atrophy, a subdural hygroma in the left frontoparietotemporal region, and hypoplasia of corpus callosum. Molecular analysis of a biopsy specimen obtained from the epidermal nevus revealed a heterozygous R248C hotspot mutation in FGFR3, whereas in normal skin the FGFR3 wild-type allele was exclusively found. The R248C mutation was also present in DNA extracted from blood leukocytes. Because FGFR3 is involved in the development of the central nervous system, the clinical and genetic findings of this case indicate a widespread mosaicism of the FGFR3 mutation. This unusual mosaic phenotype may represent a distinct entity within the group of epidermal nevus syndromes.

Epidermodysplasia verruciformis-associated and genital-mucosal high-risk human papillomavirus DNA are prevalent in nevus sebaceus of Jadassohn

BACKGROUND

The hamartoma nevus sebaceus (NS) presents at birth or early childhood as a yellowish plaque characterized histologically by variable acanthosis, papillomatosis, sebaceus hyperplasia, and proliferations of adnexal structures. Clinically apparent human papillomavirus (HPV) infection is also recognized by acanthosis and papillomatosis.

OBJECTIVE

We sought to determine the prevalence and physical state of HPV DNA in NS.

METHODS

DNA was retrieved from 44 formalin-fixed, paraffin-embedded samples of NS (22 with secondary tumors [eg, trichoblastoma, verruca, syringocystadenoma papilliferum] and two epidermal nevi [EN]). Nested polymerase chain reaction with multiple degenerate consensus and type-specific primers and direct sequencing of polymerase chain reaction products was performed. For selected cases, in situ hybridization using probes specific for HPV 5 and 8 and for high-risk genital-mucosal HPV types was performed.

RESULTS

HPV DNA was detected in 82% of NS and both EN, and consisted of genital-mucosal HPV types in 52% (HPV 6, 16, and 33) and a diverse variety of epidermodysplasia verruciformis-associated HPV types in 61%, including well-known epidermodysplasia verruciformis HPV types (5, 8, 15, 20, 22, 24, 36, 37, 38, and 80) and putatively novel epidermodysplasia verruciformis HPV types (DL285, DL287, DL436, and alb-1, -2, -3, -5, -6, -7, -8, -10, -11, -12, and -13). HPV coinfection was frequent, found in 48% (two HPV genotypes in 35% and 3 in 13%). Of NS and EN, 42% had HPV genotypes associated with cancer (ie, HPV 5, 8, 16, 20, 33, and 38); the two most commonly identified HPV types where HPV 16 (39%) and HPV 38 (18%). No differences were detected comparing frequency of HPV DNA detected with respect to age or presence of a secondary tumor. Histologically, all NS and EN showed HPV-associated cytopathic effects (ie, perinuclear halos, altered keratohyaline granules). By in situ hybridization, 64% (18/28) were positive, showing a low-intensity, punctate nuclear signal in epidermal and adnexal keratinocytes, indicating viral integration and low viral genome copy number.

LIMITATIONS

Absence of adjacent, uninvolved normal-appearing skin control samples.

CONCLUSION

HPV DNA is prevalent in NS, and HPV 16, the most frequently detected genotype, appears to be integrated into the host genome. Whether HPV represents a commensal infection caused by localized cutaneous predisposition, or is an essential factor in the pathogenesis of NS is unknown. The high frequency of oncogenic HPV types implicates maternal transmission of HPV and infection of an ectodermal stem cell leading to an epigenetic mosaic and altered skin development manifested along Blaschko's lines.

Trichilemmal cyst nevus: A new complex organoid epidermal nevus

A 31-year-old woman had an organoid nevus characterized by multiple trichilemmal cysts arranged in a bandlike pattern. The involved streaks followed Blaschko's lines and were covered, in addition, by multiple filiform hyperkeratoses and comedo-like plugs. Some histopathologic features of this complex nevus were reminiscent of those of well-established organoid nevi such as nevus comedonicus, porokeratotic eccrine nevus, or hair follicle nevus, but the presence of multiple large trichilemmal cysts was a conspicuously distinctive abnormality. Consequently, we propose for this new organoid nevus the names "trichilemmal cyst nevus" or "nevus trichilemmocysticus."

Phacomatosis pigmentokeratotica associated with a suprasellar dermoid cyst and leg hypertrophy

Phacomatosis pigmentokeratotica (PP) is a mosaic disorder that represents a distinct epidermal naevus syndrome. Its defining features are an epidermal naevus that is usually of the sebaceous type and a speckled lentiginous naevus arranged in a chequerboard pattern. In addition, there are neurological, ophthalmological and skeletal abnormalities, including limb hemiatrophy with muscular weakness, ptosis, seizures and ipsilateral segmental hyperaesthesia and hyperhidrosis. We report a 44-year-old man with an extensive epidermal naevus and an ipsilateral speckled lentiginous naevus. He also had ipsilateral right leg hypertrophy and a suprasellar dermoid cyst with associated neurological abnormalities. We propose that this case represents an unusual example of PP.

Fibroblast Growth Factor Receptor 3 Mutations in Epidermal Nevi and Associated Low Grade Bladder Tumors

Epidermal nevi (EN) are benign lesions presenting at birth or in childhood. Based on the occurrence of fibroblast growth factor receptor 3 (FGFR3) mutations in seborrheic keratosis and urothelial carcinomas (UC), and the identification of two young patients with EN and UC, we hypothesized that mutations might occur in EN. The R248C mutation was found in 6/23 (26.1%) EN but it was absent from unaffected skin. In two patients with EN and UC, both lesions were FGFR3 wild type. Our findings indicate that: (1) FGFR3 mutations occur in mosaicism and can cause EN and (2) other genes are involved in EN.

Skin adnexal neoplasms--part 1: an approach to tumours of the pilosebaceous unit

Skin adnexal neoplasms comprise a wide spectrum of benign and malignant tumours that exhibit morphological differentiation towards one or more types of adnexal structures found in normal skin. Most adnexal neoplasms are relatively uncommonly encountered in routine practice, and pathologists can recognise a limited number of frequently encountered tumours. In this review, the first of two, the normal histology of the skin adnexal structures is reviewed, and the histological features of selected but important benign and malignant tumours and tumour-like lesions of pilosebaceous origin discussed, with emphasis on the diagnostic approach and pitfalls in histological diagnosis.

Congenital linear unilateral basal cell nevus: a case report with patched gene molecular studies

BACKGROUND

Linear unilateral basal cell nevus represents a linear collection of macules and papules histologically similar to basal cell carcinoma but with benign clinical behavior. We describe a patient who initially presented at the age of 6 months with a unilateral linear basal cell nevus on the right flank. The differential diagnosis included the nevoid basal cell carcinoma syndrome. Constitutional PTCH mutations are causative of the nevoid basal cell carcinoma syndrome, and somatic PTCH mutations are found in the vast majority of basal cell carcinomas. Somatic SMO mutations have also been found in some basal cell carcinomas.

METHODS

Histologic examination of the lesions is performed. Short tandem-repeat molecular analysis at the PTCH locus and sequencing of PTCH and SMO genes is performed.

RESULTS

Histologic examination revealed features initially indistinguishable from basal cell carcinoma. Short tandem-repeat DNA analysis did not reveal loss of heterozygosity at the PTCH locus. DNA sequencing of both the PTCH and the SMO genes from the patient's lesions revealed neither inactivating mutations of PTCH nor activating mutations of SMO.

CONCLUSION

Molecular examination indicates that the PTCH and SMO genes are not involved in the pathogenesis of the patients' congenital linear unilateral basal cell nevus. Furthermore, we discuss the relationship between linear basal cell nevus and basaloid follicular hamartoma.