Neurocutaneous Syndromes and Tuberous Sclerosis — Examination Question Bank

Genetics, Molecular Biology & Diagnostic Criteria

Question	Answer
1. Explain the molecular genetics and mTOR pathway in Tuberous Sclerosis Complex (TSC).	Autosomal dominant neurocutaneous disorder characterized by benign hamartomas in multiple organ systems. - Genetic Defects: Mutations in either TSC1 on chromosome $9q34$ (encoding Hamartin) or TSC2 on chromosome $16p13.3$ (encoding Tuberin). - $pprox 65-70\%$ of cases represent spontaneous de novo mutations. - TSC2 mutations are more frequent and associated with a significantly more severe clinical phenotype. - Molecular Pathogenesis: Under physiological conditions, Hamartin and Tuberin form a heterodimeric cytosolic GTPase-activating protein (GAP) complex that inhibits Rheb (Ras homolog enriched in brain). - Rheb-GTP activates mTORC1 (mammalian Target of Rapamycin Complex 1). - Loss of either TSC1 or TSC2 relieves inhibition on Rheb, triggering uncontrolled, constitutive hyperactivation of mTORC1 kinase. - Downstream phosphorylation of S6K1 and 4E-BP1 promotes massive cell growth, proliferation, angiogenesis, and inhibition of autophagy, generating hamartomatous tumors across the brain, skin, kidneys, heart, and lungs.
2. Detail the updated International Diagnostic Criteria for Tuberous Sclerosis Complex (2012/2021).	Major Criteria (11): 1) Hypomelanotic macules ($\ge 3$, each at least $5 ext{ mm}$ diameter). 2) Angiofibromas ($\ge 3$) or fibrous cephalic plaque. 3) Ungual fibromas (Koenen tumors, $\ge 2$). 4) Shagreen patch. 5) Multiple retinal hamartomas. 6) Multiple cortical tubers and/or radial migration lines. 7) Subependymal nodules (SEN, $\ge 2$). 8) Subependymal giant cell astrocytoma (SEGA). 9) Cardiac rhabdomyoma. 10) Lymphangioleiomyomatosis (LAM). 11) Angiomyolipomas ($\ge 2$). Minor Criteria (6): 1) "Confetti" skin lesions. 2) Dental enamel pits ($>3$). 3) Intraoral fibromas ($\ge 2$). 4) Retinal achromic patch. 5) Multiple renal cysts. 6) Nonrenal hamartomas. Definite Diagnosis: 2 Major Criteria OR 1 Major + $\ge 2$ Minor Criteria, OR identification of a pathogenic mutation in TSC1 or TSC2.
3. What is the classic "Vogt Triad" and why is it historically flawed?	- Vogt's Triad consists of: Epilepsy + Mental Retardation + Adenoma Sebaceum (Facial Angiofibromas). - Clinical Pearl: This triad is present in only $pprox 30\%$ of all TSC patients and represents the severe end of the phenotypic spectrum. Many children have normal intelligence ($50\%$), subtle skin lesions, or absence of facial angiofibromas in early childhood.

Dermatological & Neurological Manifestations

Question	Answer
4. Describe the Cutaneous Features of TSC and their timeline of appearance.	1) Hypomelanotic Macules (Ash-Leaf Spots): Earliest cutaneous sign; present at birth or early infancy in $>90\%$. Lanceolate/oval, amelanotic patches best visualized using a Wood's Lamp (UVA light induces contrast between amelanotic patch and surrounding skin). 2) Facial Angiofibromas (Adenoma Sebaceum): Appear between 3 and 10 years of age. Discrete red-to-brown papules over the bridge of the nose, cheeks, and chin in a symmetrical butterfly distribution, characteristically sparing the upper lip and philtrum (distinguishing them from acne vulgaris). 3) Shagreen Patch: Appears in mid-childhood. An elevated, leathery, pebbled plaque with an "orange-peel" texture, characteristically located in the lumbosacral region. 4) Ungual Fibromas (Koenen Tumors): Appear during adolescence or adulthood. Fleshy, firm nodules emerging from under the nail bed (subungual) or lateral nail fold (periungual). 5) Forehead Fibrous Plaque: Yellow-brown, firm, fibrous plaque on the forehead or scalp.
5. What is the management of Infantile Spasms (West Syndrome) in Tuberous Sclerosis?	- Infantile spasms occur in $40-50\%$ of infants with TSC, presenting with clusters of brief myoclonic flexor/extensor spasms upon waking and hypsarrhythmia on EEG. - First-Line Drug of Choice: Oral Vigabatrin (Sabril) ($100-150 ext{ mg/kg/day}$). - Mechanism: Irreversible inhibitor of GABA transaminase, elevating brain inhibitory GABA concentrations. - In TSC, Vigabatrin achieves complete spasm cessation and EEG normalization in $>80-90\%$ of cases (significantly superior to ACTH / steroids!). - VIVA TRAP Monitoring: Vigabatrin carries a risk of permanent, irreversible concentric Visual Field Constriction. Mandatory baseline and serial visual field testing or electroretinography (ERG) every 3-6 months is required!
6. Contrast Cortical Tubers, Subependymal Nodules (SEN), and SEGA.	- Cortical Tubers: Dysplastic, disorganized glioneuronal hamartomas in cerebral cortex; primary structural generators of refractory focal seizures and epileptic encephalopathy. - Subependymal Nodules (SEN): Benign calcified nodules protruding into ventricular cavities ("candle-guttering" appearance along lateral ventricles). Asymptomatic. - Subependymal Giant Cell Astrocytoma (SEGA): Slow-growing, highly vascular benign tumors arising from SEN near the Foramen of Monro in $10-15\%$ of TSC patients (typically during childhood/adolescence). - Obstruction of CSF flow causes acute/subacute obstructive biventricular hydrocephalus, presenting with morning headaches, vomiting, lethargy, papilledema, and visual deterioration.

Visceral Involvement, mTOR Inhibitors & Viva Traps

Question	Answer
7. Describe Renal Angiomyolipomas (AML) and the risk of Wunderlich Syndrome.	- Renal AMLs are benign triphasic hamartomas composed of dysplastic blood vessels, smooth muscle, and mature adipose tissue, present in $>75-80\%$ of TSC patients by adulthood. - Complications: Progressive renal parenchymal compression leading to CKD; aneurysm formation in dysplastic aneurysmal vessels. - Wunderlich Syndrome: Spontaneous retroperitoneal hemorrhage from ruptured AML aneurysms. Risk of life-threatening bleeding escalates exponentially when AML diameter exceeds $>3-4 ext{ cm}$ or aneurysms exceed $>5 ext{ mm}$! - Contiguous Gene Deletion Syndrome: Contiguous deletion of TSC2 and the adjacent PKD1 gene on chromosome 16 causes early, severe Polycystic Kidney Disease presenting in infancy with massive bilateral kidney enlargement, severe hypertension, and rapid renal failure.
8. What are the Indications for mTOR Inhibitors (Everolimus / Sirolimus) in TSC?	Everolimus (oral mTORC1 inhibitor) provides disease-modifying, targeted therapy for: 1) SEGA: First-line medical therapy for growing SEGA not requiring emergency neurosurgical decompression. 2) Renal Angiomyolipomas: Treatment of choice for asymptomatic AMLs $>3-4 ext{ cm}$ to induce tumor shrinkage and prevent hemorrhagic aneurysm rupture. 3) Refractory Focal Epilepsy: Adjunctive therapy for drug-resistant focal onset seizures in TSC patients $\ge 2$ years. 4) Pulmonary Lymphangioleiomyomatosis (LAM): Stabilizes lung function and arrests cystic destruction.
9. VIVA TRAP: What is the natural history of Cardiac Rhabdomyomas in TSC?	- Cardiac rhabdomyomas are intracardiac hamartomas detected in $>60-80\%$ of infants with TSC (often detected antenatally on fetal echocardiography). - Natural History: Spontaneous Regression occurs in $>90\%$ of cases during early childhood as maternal estrogen influence wanes and cardiomyocytes mature! - Clinical Approach: Conservative observation unless causing severe ventricular outflow tract obstruction or refractory arrhythmias (e.g., Wolff-Parkinson-White syndrome). Surgery is rarely required.