Naevus sebaceous

• Relatively common among ENS.
• Skin lesions are salmon or yellow colour and waxy.
• Epilepsy and intellectual impairment are common.

Keratinocytic epidermal naevus

• Again, relatively common.
• Pink or hyperpigmented plaques.
• Intellectual impairment, structural brain abnormalities, skeletal abnormalities and strabismus are reported.

Naevus comedonicus

• Skin lesions are localised collections of dilated follicles containing keratin, which may become infected or inflamed.
• EEG abnormalities, cataracts and skeletal abnormalities are reported.

Congenital hemidysplasia, ichthyosiform naevus and limb defects syndrome

• Congenital unilateral ichthyosiform erythroderma is the synonym.
• CHILD is the acronym for Congenital Hemidysplasia, Ichthyosiform Naevus and Limb Defects.
• Skin lesions are unilaterally inflammatory, reddened patches which may have dry scales; they are often located in the skinfolds.
• Ipsilateral hypoplasia of limbs can occur; the axial skeleton may also be affected.
• EEG abnormalities and hemispheric brain hypoplasia and cardiac abnormalities are reported.

Becker's naevus (pigmented hairy epidermal naevus)

• A patch of hyperpigmentation and hypertrichosis, which is androgen-dependent and so becomes more prominent after puberty in males; usually located on the shoulder.
• Onset is usually in late childhood/adolescence.
• Associated with skeletal abnormalities, underlying muscle hypoplasia and ipsilateral hypoplasia of the breast.

Proteus syndrome

• Variable clinical features, characterised by overgrowth of multiple tissues.
• CNS involvement is not typical, but seizures and intellectual impairment have been reported.
• Other possible features are ovarian or parotid tumours, lipomas and vascular malformations.
• There are diagnostic criteria.

Phacomatosis pigmentokeratotica

• A speckled lentiginous naevus associated with an epidermal naevus. The melanocytic component usually follows a segmental pattern ('checkerboard pattern') rather than following the lines of Blaschko.
• There may be neurological, ocular and skeletal abnormalities.
• Hemiatrophy with muscle weakness is common.

Inflammatory linear verrucous epidermal naevus

• Skin lesions are linear, pruritic, reddened and hyperkeratotic papules or plaques.
• Usually unilateral on the lower half of the body, often the buttock.
• Often presents at <6 months of age.
• May resemble psoriasis.
• There may be associated skeletal abnormalities, although this point has been questioned.

Porokeratotic eccrine naevus

• Verrucous, keratotic papules on the palms and soles.
• There may be widespread cutaneous involvement.

Aetiology

The lesions probably arise from abnormal ectodermal cells in the embryo.^[4] Ectodermal cells give rise to the skin epidermis and to neural tissue. Mosaicism seems to be involved, ie there are genetically different cell lines in one individual, and the abnormal cells give rise to the lesions.

A detailed review of the genetic basis and pathogenesis of ENS is available.^[2]

Visual appearance

Epidemiology

Epidermal naevi (with or without other organ involvement) have an incidence of around 2 per 1,000 live births.^[2] Epidermal naevus syndromes (ENS) are all very uncommon, without reliable population incidence figures. Of patients with epidermal naevi, 10-30% may have disorders in other organs suggesting an ENS.^[5][6]

Presentation

• Their most common forms are probably the sebaceous naevus (affecting the scalp), and the verrucous epidermal naevus. This has the appearance of verrucous papules that coalesce to form well-demarcated papillomata, ranging in colour from that of the surrounding skin to much more deeply pigmented.
• They may be congenital lesions, or develop during the early years of life. They tend to grow during childhood and then stabilise during the teenage years.^[1]
• They may be localised to a small area or occur in more diffuse forms. They are often arranged in a linear fashion along skin tension lines or the lines of Blaschko (purported lines of epidermal growth derived from clonal tissue patterns thought to be formed in embryo).^[7]
• The lesions themselves are usually asymptomatic apart from their appearance. However, inflammatory linear verrucous epidermal naevus (ILVEN) lesions may be inflamed and irritated; naevus comedonicus lesions may become infected or inflamed.

In epidermal naevus syndrome (ENS), neurological involvement may include:

• Epilepsy or infantile spasms.
• Intellectual impairment.
• Structural or vascular brain abnormalities.
• Spinal lesions.

Skeletal involvement includes:

• Incomplete formation of bony structures, eg spina bifida.
• Hypoplasia of bones.
• Bony cysts.
• Asymmetry of the skull or spine.
• Spontaneous fractures and rickets.

Ophthalmic involvement includes:

• Colobomas.
• Strabismus.
• Ptosis.
• Nystagmus.
• Corneal opacities.
• Retinal changes.
• Various other ocular abnormalities which have been described.

Endocrine features have been reported:

• Hypophosphataemic vitamin D-resistant rickets has occurred in a number of cases.^[8]
• Precocious puberty has been described in several cases.
• Syndrome of inappropriate antidiuretic hormone (SIADH) has been reported in one case.

Differential diagnosis

• Sebaceous naevus
• Naevus syringocystadenomatosus papilliferus
• Juvenile xanthogranulomata
• Solitary mastocytoma
• Multiple melanocytic naevi
• Other skin and CNS lesions, e.g:
  • Sturge-Weber syndrome
  • Tuberous sclerosis
  • Neurofibromatosis
  • McCune-Albright syndrome

Assessment

Initial assessment, to include exclusion of an epidermal naevus syndrome (ENS):^[2]

• Full developmental and family history.
• Careful examination of all skin lesions. Skin biopsy may be required.
• Neurological examination.
• Ophthalmic examination.
• Assess skeleton, symmetry and gait.

Consider if further assessment required:

• Generally, children with small epidermal naevi and no other findings do not need further investigation, although skin biopsy should be considered.^[2]
• Large epidermal naevi, especially in the head and neck, may merit CNS assessment.
• Epidermal naevi should be fully assessed if there is a suspected syndrome involving other organs.

Investigations

These should be based on the needs of the individual patient, but may include:^[9]

• Skin lesions should be referred for dermatological assessment and/or biopsied to ascertain their nature.
• CT/MRI are used to assess the presence/degree of any intracerebral or intraspinal lesion.^[10]
• Plain X-rays, eg skull X-ray, CXR or skeletal survey.
• EEG.
• Biochemistry and endocrine investigations: these may be appropriate, eg renal function, electrolytes, calcium and phosphate.

Management

Skin lesions

• Depending on the location and size of the lesions, excision may be merited for cosmetic reasons, but may not be feasible if underlying structures are involved.
• Other possible treatments are:
  • Laser treatment may be successful in some cases.
  • Topical vitamin D (calcipotriol) may be helpful in treating inflammatory linear verrucous epidermal naevus (ILVEN), although there is conflicting evidence about its effectiveness.
  • 5-fluorouracil was used with good results in one case of a large linear epidermal naevus.
  • Tacrolimus and fluocinonide, in combination, were successfully used in one case of ILVEN.^[11]
  • Shave excision followed by phenol peeling was used with good outcome in one case of verrucous epidermal naevus.
• If there is new growth of the skin lesion, excisional biopsy may be indicated to rule out malignancy.

CNS lesions

• Anticonvulsants for epilepsy.
• Neurosurgery has been used in a few selected cases to control epilepsy.^[12]

Complications

• Poor cosmetic appearance.
• Inflammation of the lesion in certain forms (inflammatory linear verrucous epidermal naevus (ILVEN)).
• Benign or malignant tumours arising within the lesion.

Prognosis

The prognosis is very good. They have the potential to have benign appendageal tumours arise within them (often syringocystadenoma papilliferum), or to transform into malignant tumours such as basal cell carcinoma or squamous cell carcinoma.

The lifetime risk of malignant transformation in sebaceous naevi is thought to be less than 1%.^[13] Malignant transformation of the lesion is rare before adolescence/adulthood.

Verrucous epidermal naevi seem to have a much lower chance of forming tumours.^[1]