DIFFUSE EPIDERMOLYTIC EPIDERMAL NEVUS AND GENETIC COUNSELING: A CASE REPORT AND BRIEF REVIEW OF THE TOPIC Diffuse Epidermolytic Epidermal Nevus and Genetic Counseling: A Case Report and Brief Review of the Topic

A 16-month-old female presented with an extensive epidermal nevus demonstrating epidermolytic hyperkeratosis on histologic evaluation. Individuals with this disorder are at increased risk of bearing children with epidermolytic ichthyosis. This occurs because the same mutations causing cutaneous somatic mosaicism may also affect the gonads. Genetic counseling is advised for individuals with extensive epidermolytic epidermal nevus, as the generalized epidermolytic hyperkeratosis carries significant morbidity and mortality. Introduction Epidermal nevi are a class of hamartomas derived from ectoderm. They are relatively common, affecting 1 in 1,000 individuals. They may present as a single plaque or be more extensive, assuming a whorled appearance. This type of arrangement is also known as a Blaschkoid pattern, which is frequently seen in skin conditions displaying genetic mosaicism.1 Genetic mosaicism occurs when two genetically distinct cell populations proliferate in one organism. This can result in two or more phenotypically unique cutaneous lesions, as in the case of epidermal nevi.2 Keratinocytic epidermal nevi are those derived from ectoderm that goes on to differentiate into keratinocytes. There are more than 10 histologically distinct types of keratinocytic nevi. One such variant demonstrates epidermolytic hyperkeratosis and is thus known as an epidermolytic epidermal nevus. This entity is clinically indistinguishable from other subtypes within this category.3 Uniquely, this histologic finding is also seen in a generalized form, known as epidermolytic ichthyosis or bullous congenital ichthyosiform erythroderma. Generalized epidermolytic ichthyosis an autosomaldominantly inherited condition with significant associated morbidity and mortality, resulting from a mutation in the genes that code for keratins (K) 1 and 10. These same defects have been demonstrated in epidermolytic epidermal nevi in individuals who have born offspring with epidermolytic hyperkeratosis. This indicates that this postzygotic mutation may also result in gonadal mosaicism, especially in individuals with extensive lesions. We present a case of a patient with an extensive epidermolytic epidermal nevus to highlight the importance of genetic counseling, as these patients are at heightened risk for bearing children with epidermolytic ichthyosis. Case Report A 16-month-old Iraqi immigrant presented to the clinic with her parents for evaluation of a skin eruption. The lesions appeared when she was 3 weeks old and developed on her neck, arms, flanks, abdomen, and legs. The rash initially was red and scaly with no noted blisters. It was initially treated with triamcinolone acetonide 0.1% ointment, which improved the pruritus but did not alter the morphology of the lesions. Since the initial appearance of the lesions, some of the areas had become brown and scaly, others brown and warty. The mother reported an uneventful pregnancy and birth. The patient was the youngest of four sisters, none of whom had similar lesions. There was no family history of consanguinity, and the parents denied any members of the extended family with similar markings. On presentation to the clinic, the patient was being treated with isoniazid for latent tuberculosis. She was otherwise a healthy, well-developed toddler. Her parents denied a history of cognitive or developmental delays. They were concerned that the lesions were a result of a chicken pox vaccine she received in Iraq. On physical exam, the patient was an alert 16-month-old in no acute distress. On cutaneous examination, there were whorled plaques of various morphologies in a Blaschkoid arrangement distributed on her neck, bilateral upper extremities, flanks, abdomen, and bilateral medial thighs (Figure 1). Verrucous brown papules coalesced into linear plaques on the left anterior neck, bilateral axillae, and crural folds. On the flanks were digitate erythematous plaques with white scale. A hyperpigmented plaque with large, plate-like, brown scale was located on the left lateral leg. No apparent unilateral hemihypertrophy of the limbs or dysmorphic facies was appreciated. Shave biopsies were obtained from a verrucous lesion of the left axilla and from an eczematous lesion on the left flank. These were submitted in formalin for standard pathologic evaluation