Thyroid Eye Disease

The bony orbit is a fixed-volume space containing the globe, extraocular muscles, orbital fat, and the optic nerve at its apex. Thyroid eye disease (TED), or Graves' orbitopathy, is an immune-mediated orbital disorder most commonly associated with Graves' hyperthyroidism, in which orbital tissue expansion within this fixed space produces proptosis and, when severe, optic nerve compression.

TED results from autoantibodies (most notably against the TSH receptor, shared by thyroid follicular cells and orbital fibroblasts) triggering inflammation and glycosaminoglycan deposition in orbital fat and extraocular muscles, causing tissue expansion, muscle enlargement, and fibrosis. This expansion within the fixed bony orbit produces proptosis and can compress the optic nerve at the orbital apex (dysthyroid optic neuropathy) or restrict extraocular muscle function (restrictive strabismus, classically involving the inferior rectus).

Presentation includes eyelid retraction, asymmetric proptosis, redness/chemosis, diplopia (worse in specific gaze positions), and, in severe cases, progressive vision loss. Headache can be a presenting feature relevant to neurologists.¹

Key differentials: orbital cellulitis/inflammatory disease, orbital mass lesion (lymphoma, metastasis) causing unilateral proptosis, myasthenia gravis (lacks restrictive motility pattern), and idiopathic orbital inflammation (different imaging, normal thyroid function).

Structured orbital examinations using the Clinical Activity Score (pain, redness, swelling) and EUGOGO severity/activity categories stage disease and guide management.¹ Exophthalmometry objectively measures proptosis; motility exam assesses restrictive strabismus pattern; visual acuity, color vision, pupillary exam, and visual fields screen for optic neuropathy.

Key foundational steps for all patients: restoring euthyroidism, smoking cessation, and serial orbital examinations.¹ Vision loss from dysthyroid optic neuropathy requires urgent high-dose IV glucocorticoids and early orbital decompression.¹ Active inflammatory disease is treated with IV methylprednisolone plus mycophenolate, or teprotumumab (the first FDA-approved targeted TED therapy, effective for reducing proptosis and inflammation).¹² Teprotumumab carries an increasingly recognized risk of ototoxicity (bilateral high-frequency SNHL, tinnitus, aural fullness, often after 3-6 infusions, sometimes persistent), with no standardized monitoring protocol yet established.²

• Euthyroidism restoration and smoking cessation are foundational for every TED patient¹
• Dysthyroid optic neuropathy is a sight-threatening emergency requiring urgent IV glucocorticoids and decompression¹
• Clinical Activity Score and EUGOGO staging should guide treatment, not just describe disease¹
• Teprotumumab is effective but carries a recognized, potentially irreversible ototoxicity risk²
• Common pitfall: delaying recognition of optic neuropathy, missing the window for vision-preserving treatment
• Common pitfall: prescribing teprotumumab without counseling on auditory risk or baseline hearing assessment