Thyroid Eye Disease

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Pathophysiology & Risks - Genesis of Graves' Gaze

  • Autoimmune: Graves' disease; T-cell mediated.
  • Mechanism: TSH-Receptor Antibodies (TRAb) target TSH-R on orbital fibroblasts.
    • Fibroblast activation: ↑ proliferation, differentiation.
    • ↑ Glycosaminoglycan (GAG) production (hyaluronan) → edema.
    • ↑ Adipogenesis (fat cell formation).
  • Outcome: Orbital tissue expansion, muscle swelling, inflammation, fibrosis.
  • Risk Factors:
    • Smoking (strongest modifiable).
    • Female sex.
    • Genetics (HLA-DR3).
    • Radioiodine therapy (can worsen).

⭐ Key pathogenic mechanism: autoantibodies against TSH receptor (TSH-R) on orbital fibroblasts, leading to glycosaminoglycan accumulation and adipogenesis.

Thyroid Eye Disease Pathophysiology

Clinical Features - The Proptotic Profile

  • Proptosis (Exophthalmos):
    • Hallmark of TED; bilateral, often asymmetric.
    • Hertel: Normal < 21mm (Caucasians), < 18mm (Asians); inter-eye > 2mm diff. significant.
    • Severity: Mild (21-23mm), Mod. (24-27mm), Severe (>28mm).
  • Key Eyelid Signs:
    • Lid Retraction (Dalrymple's): Most common; sclera above limbus.
    • Von Graefe's: Lid lag (downgaze).
    • Stellwag's: Infrequent blinking.
  • Soft Tissue:
    • Eyelid/periorbital edema.
    • Conjunctival injection (over recti), chemosis.

Exophthalmos (proptosis) is the hallmark of TED; lid retraction (Dalrymple's sign) is the most common ocular sign.

Classification - Staging the Stare

NOSPECS Classification (Severity) 📌

  • Grades manifestations:
    ClassFinding
    0No signs/symptoms
    IOnly signs (lid retraction)
    IISoft tissue
    IIIProptosis (>22mm)
    IVEOM involvement
    VCorneal
    VISight loss (Optic Neuropathy)

Clinical Activity Score (CAS) (Activity)

  • Active: ≥3/7 or ≥4/10. 1 point/sign.
    Original CAS (7 signs)Expanded adds (3 signs)
    Pain (spontaneous/gaze)↑ Proptosis ≥2mm
    Eyelid redness/swelling↓ Motility ≥8°
    Conj. redness/chemosis↓ VA ≥1 line
    Inflamed caruncle/plica

⭐ The Clinical Activity Score (CAS) is essential for determining active inflammation and guiding immunosuppressive therapy.

Investigations - Unmasking Orbitopathy

  • Thyroid Function Tests (TFTs): TSH, fT3, fT4.
  • Autoantibodies:
    • TSH Receptor Antibodies (TRAb) - key diagnostic marker.
    • Anti-Thyroid Peroxidase (Anti-TPO) Antibodies.
  • Orbital Imaging:

    CT or MRI of the orbits typically reveals fusiform enlargement of extraocular muscle bellies with sparing of the tendons.

    • Assesses Extraocular Muscles (EOMs) (📌 IMSLO: Inferior > Medial > Superior > Lateral > Obliques), optic nerve. Axial CT orbits: Thyroid eye disease with muscle enlargement
  • Functional Tests: Visual fields, color vision (for optic neuropathy).

Management - Calming the Crisis

  • Supportive: Smoking cessation, lubricants, selenium.
  • Activity: CAS (Clinical Activity Score; active if ≥3/7).
  • Severity: NOSPECS / EUGOGO. (📌 NO SPECS: No signs/symptoms, Only signs, Soft tissue, Proptosis, EOM involvement, Corneal, Sight loss).

Sight-threatening dysthyroid optic neuropathy (DON) is an ophthalmic emergency managed with urgent high-dose systemic corticosteroids (e.g., IV methylprednisolone).

High‑Yield Points - ⚡ Biggest Takeaways

  • Thyroid Eye Disease (TED) is the most common cause of proptosis in adults, often bilateral.
  • Strongest association with Graves' disease; mediated by TSH receptor antibodies.
  • NOSPECS classification is used for severity; optic neuropathy is the most serious complication.
  • Classic signs include lid retraction (Dalenrymple's) and lid lag (Von Graefe's).
  • Inferior rectus is the most frequently affected extraocular muscle, then medial rectus.
  • Treatment aims to manage activity and severity: steroids, radiotherapy, surgical decompression.

Practice Questions: Thyroid Eye Disease

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What is the most common cause of intermittent proptosis in adults?

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Flashcards: Thyroid Eye Disease

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Upper lid crease is _____ in aponeurotic ptosis

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Upper lid crease is _____ in aponeurotic ptosis

present

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