Random Dermatology MCQ - Epidermal Nevus syndrome

A 6-month-old infant presents with a linear, verrucous, brown plaque along the lines of Blaschko on the right side of the trunk and limb, present since birth. The child has also had infantile spasms. An MRI of the brain would most likely reveal which of the following findings, and what is the most common associated skeletal anomaly?

A. Hemimegalencephaly; most commonly associated with kyphoscoliosis.
B. Tuberous sclerosis cortical tubers; most commonly associated with bone cysts.
C. Sturge-Weber leptomeningeal angioma; most commonly associated with limb hypertrophy.
D. Neurofibromatosis optic pathway glioma; most commonly associated with sphenoid wing dysplasia.
E. Linear nevus sebaceus on the scalp; most commonly associated with frontal bossing.

Correct Answer: A. Hemimegalencephaly; most commonly associated with kyphoscoliosis.

Answer and Explanation

The correct answer is A. This question describes a classic presentation of Epidermal Nevus Syndrome (ENS), also known as Linear Sebaceous Nevus Syndrome when the nevus is organoid. The key clues are the congenital linear epidermal nevus following Blaschko's lines and the neurological symptom of infantile spasms. The most frequent and serious central nervous system abnormality in ENS is hemimegalencephaly (unilateral overgrowth of a cerebral hemisphere), which is a common cause of the intractable seizures. Regarding skeletal anomalies, kyphoscoliosis is the most common, though a wide variety of bone dysplasias can occur.

Why the Other Options are Incorrect:

• B. Tuberous sclerosis cortical tubers: While tuberous sclerosis can cause seizures and skin lesions (ash-leaf spots, facial angiofibromas), the skin finding described is a linear Blaschkoid epidermal nevus, not hypomelanotic macules. Cortical tubers are not specific to ENS.

• C. Sturge-Weber leptomeningeal angioma: Sturge-Weber syndrome presents with a port-wine stain (capillary malformation) in the trigeminal distribution, not a linear verrucous plaque. It is associated with seizures and glaucoma.

• D. Neurofibromatosis optic pathway glioma: Neurofibromatosis type 1 presents with café-au-lait macules and neurofibromas, not linear epidermal nevi. Sphenoid wing dysplasia is associated with NF1, not ENS.

• E. Linear nevus sebaceus on the scalp...: While a linear nevus sebaceus on the scalp is a common presentation of ENS, this option incorrectly identifies it as the MRI finding. Furthermore, frontal bossing may occur, but kyphoscoliosis is the most common skeletal anomaly.

Additional High-Yield Information for Exams:

• Definition: ENS is a sporadic neurocutaneous disorder characterized by the presence of an epidermal nevus (any type: verrucous, sebaceous, keratinocytic) and associated multisystem involvement, primarily of the CNS, eyes, and skeleton.

• Spectrum & Genetics: ENS is now understood as a mosaic disorder. Somatic postzygotic mutations in genes involved in the RAS/MAPK pathway (e.g., HRAS, KRAS, NRAS, FGFR3) have been identified in both the nevi and affected internal tissues, explaining the segmental distribution and multi-organ involvement.

• Clinical Features:

  • Skin: The epidermal nevus is present at birth or appears in early childhood. It is typically linear along Blaschko's lines and can be anywhere on the body.

  • Neurologic (50-75%): Seizures (most common, often intractable), intellectual disability, hemiparesis, and hemimegalencephaly. The risk is highest with nevi on the face or head.

  • Skeletal (30-70%): Kyphoscoliosis, limb length discrepancy, vitamin D-resistant rickets (due to renal phosphate wasting).

  • Ocular (30-50%): Lipodermoids, colobomas, strabismus.

• Differential Diagnosis: Other neurocutaneous syndromes with linear skin lesions include: Hypomelanosis of Ito (linear hypopigmentation), Incontinentia Pigmenti (linear vesicles/verrucous plaques in females), and CHILD syndrome (unilateral inflammatory nevus with ipsilateral limb hypoplasia).

• Prognosis: Highly variable, depending on the extent of neurological and systemic involvement. Seizure control is a major challenge. Morbidity is significant in severe cases.

• Management & Rationale:

  • Rationale: Multidisciplinary management focused on controlling seizures, screening for associated anomalies, and providing supportive care.

  • First-line Investigations:

    • Neurologic: Brain MRI to assess for hemimegalencephaly and other malformations. EEG for seizure characterization.

    • Skeletal: Spinal radiographs to screen for scoliosis.

    • Ophthalmologic: Formal eye exam.

    • Renal: Serum calcium, phosphate, alkaline phosphatase to screen for rickets.

  • Treatment:

    • Neurologic: Aggressive management of seizures with anti-epileptic drugs. In cases of refractory seizures due to hemimegalencephaly, hemispherectomy may be considered.

    • Dermatologic: Treatment of the nevus is often cosmetic (excision, laser, topical retinoids) but does not affect systemic disease.

    • Other: Orthopedic care for scoliosis, vitamin D/phosphate supplementation for rickets.