epidermal nevi are hamartomatous proliferations of the epithelium , including keratinocytes , sebocytes , pilosebaceous units , eccrine glands , or apocrine glands . verrucous epidermal nevi ( ven ) are non - inflammatory keratinocytic hamartomas composed of keratinocytes . vens are characterized by linearly arranged , closely set , gray - brown to black verrucous papules . the term systematized denotes many linear lesions limited to one side of the body or having a bilateral symmetrical distribution . the histological changes of ven are variable hyperkeratosis , acanthosis and papillomatosis . apart from this usual picture there are some rarer histological patterns including epidermolytic hyperkeratosis . epidermal nevi of the epidermolytic type are rare and represent mosaic expression of epidermolytic hyperkeratosis also known as linear or nevoid bullous ichthyosiform erythroderma ( bie ) . we hereby report a case of extensive bilaterally symmetrical systematized epidermal nevus occurring along the lines of blaschko and showing epidermolytic hyperkeratosis on histology in a 3-year - old boy for the rarity of the entity . a 3-year - old boy , the only child of a non - consanguineous parentage , presented with widespread warty eruption all over the body including the genitalia but sparing the scalp , face and palms and soles . the eruption began when the child was 3 weeks of age with lesions appearing first symmetrically over anterior thigh , and then over the axillae , and within a period of about 6 months progressed to attain the present distribution . examination showed multiple , bilaterally symmetrical , verrucous plaques along the lines of blaschko extensively involving the trunk and extremities [ figure 1 ] . the linear plaques ran transversely over the trunk and longitudinally over the limbs [ figures 2 and 3 ] . focal epidermolytic hyperkeratosis was evident in the form of perinuclear vacuolization of keratinocytes of the upper epidermis with coarse keratohyaline granules [ figure 4 ] . based on the characteristic clinical and histopathological features , a diagnosis of bilateral , systematized epidermolytic verrucous epidermal nevus was made . bilaterally symmetrical verrucous plaques along the lines of blaschko symmetrical , linear verrucous plaques along the lines of blaschko over the buttock and back of thighs transversely arranged , bilaterally symmetrical linear verrucous plaques over the back histopathology showing massive hyperkeratosis and focal granular degeneration of the epidermis . epidermal nevi of all types are considered an expression of genetic mosaicism arising from somatic mutation in the affected skin but sparing the unaffected skin . the most common pattern of keratinizing epidermal nevi is verrucous epidermal nevus presenting as verrucous , serpiginous plaque following the lines of blaschko . bilaterally symmetrical involvement is also called ichthyosis hystrix . while there are many histologic variants of the epidermal nevus , most cases demonstrate variable degrees of hyperkeratosis , acanthosis , and papillomatosis . rare histological variants include epidermolytic hyperkeratosis and variants resembling acrokeratosis verruciformis , verruca vulgaris , darier disease , porokeratosis , seborrheic keratosis or psoriasis . identical histology of epidermolytic ven and bie results from a clone of cells expressing a mutation in one of the bie genes krt 1 and krt 10 in the former . bie , a rare autosomal dominant disorder , presenting as severe blisters and erythroderma at birth which usually subsides as the child grows and is replaced by appearance of thick , dark , hyperkeratotic skin especially on joints , apposed skin , scalp and neck for the rest of life . by analogy with bie , patients of epidermolytic ven are expected to be blistered at birth but they do not show such tendency , which was also evident in our case . epidermolytic ven occurs sporadically and is not heritable , but a parent with such nevus may have gonadal mutation as well and can produce offspring with classical bie . although ven may be associated with cerebral and other internal manifestations in the form of  epidermal nevus syndrome , epidermolytic variety is not associated with extracutaneous abnormalities as in our case as keratin genes are expressed only in the epithelia . the clinical differentials of systematized epidermolytic ven include non - epidermolytic ven , verrucous stage of incontinentia pigmenti , ichthyosis bullosa of siemens , and ichthyosis hystrix of curth and macklin . incontinentia pigmenti produces systematized lesions along the lines of blaschko and characteristically evolves through four clinical stages ( bullous , verrucous , hyperpigmentation , and hypopigmentation ) and exhibits eosinophilic spongiosis on histology . ichthyosis bullosa of siemens is caused by mutation of keratin 2 gene and may show mild phenotype of bie . ichthyosis hystrix of curth macklin may show systematized rigid spiky hyperkeratosis and its histopathology exhibits non - specific features of hyperkeratosis , acanthosis , and papillomatosis without epidermolysis . epidermolytic hyperkeratosis ( ehk ) refers to the combination of compact hyperkeratosis , perinuclear vacuolization of keratinocytes of the upper layers of epidermis , and coarse keratohyalin granules . these changes may occur incidentally in a large number of acquired benign and malignant conditions . however , only two congenital conditions besides bie may show these changes : ichthyosis bullosa of siemens and epidermolytic palmoplantar keratoderma of vorner . associated bacterial overgrowth can be treated with antibacterial soaps and when necessary , oral antibiotics . topical agents have a limited role and various agents had been used to decrease the hyperkeratosis . these include preparations containing salicylic acid , lactic acid , retinoic acid , 5-fluorouracil , calcipotriol and calcitriol . oral and topical retinoids have also been shown to improve patients with ehk although retinoids may promote desquamation and exacerbate blistering . continuous - wave carbon dioxide laser vaporization has been used with benefit for extensive ven . we reported a case of extensive , bilaterally symmetrical , systematized verrucous epidermal nevus of epidermolytic variety .
verrucous epidermal nevi are congenital , noninflammatory cutaneous hamartomas composed of keratinocytes . 
 they follow the lines of blaschko and show hyperkeratosis without cellular atypia . 
 the routine histology shows variable amount of hyperkeratosis , acanthosis and papillomatosis and rarely epidermolytic hyperkeratosis . 
 we saw a 3-year - old boy with bilaterally symmetrical , systematized verrucous plaques along the lines of blaschko extensively involving the trunk and extremities but sparing the face and palmoplantar skin . 
 histopathology showed features of epidermal nevi with prominent epidermolytic hyperkeratosis . 
 we report here the case for the rarity of this entity .