What is Epidermal Naevus?

 What is an epidermal naevus ?

An epidermal naevus is due to an overgrowth of the epidermis . Lesions are present at birth  or develop during childhood . The abnormality arises from a defect in the  ectoderm, the outer  layer of the embryo  that gives rises to epidermis and neural tissues . An epidermal nervus is an abnormal , noncancerous patch of skin caused by an  overgrowth of cells in the outermost layer of skin . Epidermal nevi are typically seen at birth or develop in early childhood . the epidermal is composed  primarily  of a specific cell type called  a keratinocyte . the lines of Blaschko , which are normally invisible on skin develops before birth .  Keratinocytic epidermal nevi are also known as  linear epidermal nevi or verrucous epidermal nevi , based on characteristics of their  appearance . 



There are several types of epidermal nervus that are defined in part by the type of  epidermal cell involved . The epidermal  is composed primarily of a specific cell type called a keratinocyte.  They  can be  flat , tan or brown  patches  of skin  or raised  velvety patches . some affected individuals have only an epidermal  nervus  also  have problems in other  body  systems  , such as the brain , eyes  or bones . There  are several  different  epidermal  nervus syndromes characterized by the type of epidermal nerus involved . 


What are types of epidermal naevus ? 

The skin lesions most often referred  to as epidermal  naevi  are due to an overgrowth of keratinocytes . 
- Linear epidermal naevus 
- Epidermolytic epidermal naevus 
- Acantholytic  epidermal naevus 
- Linear porokeratosis 
- systematised epidermal naevus 

What are the causes of  epidermal naevus ?

There are 2 copies of every gene, one derived from the individuals mother and the other from their  father . There are two population of skin cells , containing either the mother 's genes or the father 's genes  or the father's genes or the father 's genes . Epidermal naevi very rarely affect  more than one member  of the family . Mutations have been detected  in FGFR3 , PIK3CA  and  HRAS . Epidermal naevus are distrubted   along the lines of Blashko . The  abnormal gen is found in the epidermal naevus  cells but not in the normal skin.  The  same keratin  ten gene abnormalities have been found in parents  who have  epidermolytic epidermal naevus  and in their offspring  who have bullous  ichthyosiform erythroderma. 
The ATP2A2 gene abnormality that arises in darier  disease has been detected in the affected . 


Features of epidermal naevus :

1. Linear epidermal naevus :  
An  epidermal naevus usually arises on the trunk and limbs and is uncommon  on the face or scalp . When they first appear at birth or in infancy , they are flat tan or brown marks , but as the child ages ,  they become  thickened and often warty. The naevus may also become more extensive  for a few years   . 

2. Systematised epidermal naevus :
Systematised epidermal naevus are less common  and are sometimes known as  ichthyosis hystrix . There are multiple lesion that usually arise in a swirled pattern , arising on one or both sides  of the body . In some patients , there are also other congenital  abnormalities , particularly of the skeleton and central nervous system {ENS }. 

3. Histology of epidermal naevus :
The rare epidermolytic epidermal naevus subtype is characterised  by a specific histological pattern called epidermolytic hyperatosis and resembles that seen in bullous ichthyosiform erythroderma . Acantholytic epidermal  naevus has pathology  that resembles  darier disease . Linear porokeratosis has pathology that resembles disseminated superficial actinic porokeratosis . 



Signs & Symptoms :

Epidermal naevus syndromes  encompass a wide variety of disorder . the specific symptoms present , severity and prognosis can vary greatly depending on the specific types of Ens and the presences and extent of associated extra cutaneous  symptoms . The onset and progressive of these disorders varies greatly as well . Epidermal nevi have also been classified as harmartomas a rather vague and ambiguous term for benign tumor like malformations  that can affect any area of the body . Epidermal nevi often occur on the trunk , limbs , face  or scalp. Epidermal nevi can be striking and obvious in appearance or subtile and easy to miss . 



Generally epidermal  nevi on the head and face are more likely to be associated with malformations of the brain , eyes and cranial bones . Epidermal naevi on the trunk are more likely to be associated with abnormal  curvature of the spine hip malformation and deformities of the arms are legs . 

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