Thyroid Eye Disease

Overview

Thyroid eye disease (TED), also known as Graves' orbitopathy or thyroid-associated orbitopathy, is an immune-mediated orbital disorder most commonly occurring in association with Graves' disease hyperthyroidism, though it can also occur with euthyroid or hypothyroid states. It is increasingly encountered not only by ophthalmologists but by neurologists and other specialists, given its potential to present with optic neuropathy, diplopia, and headache.¹

Epidemiology & Risk Factors

TED most commonly occurs in the setting of Graves' hyperthyroidism, reflecting a shared autoimmune process targeting antigens common to the thyroid gland and orbital tissues. Smoking is one of the most significant modifiable risk factors for both the development and severity of TED, and smoking cessation is a foundational component of management regardless of disease activity or severity.¹ Achieving and maintaining euthyroidism is similarly a foundational early management step, since uncontrolled thyroid dysfunction (either hyper- or hypothyroid) is associated with worse TED outcomes.¹

Pathophysiology

TED results from an autoimmune process in which autoantibodies (most notably against the thyroid-stimulating hormone receptor, shared by thyroid follicular cells and orbital fibroblasts) trigger inflammation and glycosaminoglycan deposition within the orbital fat and extraocular muscles, causing orbital tissue expansion, muscle enlargement, and fibrosis over time. This expansion within the fixed bony orbit produces proptosis and, when severe, compresses the optic nerve at the orbital apex (dysthyroid optic neuropathy) or restricts extraocular muscle function (causing diplopia from restrictive strabismus rather than a primary neuromuscular problem).

Clinical Presentation

Patients may present with a range of findings depending on disease activity and severity: eyelid retraction and a "staring" appearance, proptosis (often asymmetric), redness and chemosis from orbital congestion, diplopia (typically worse in specific gaze positions reflecting the pattern of muscle involvement, classically the inferior rectus), and, in severe cases, progressive vision loss from optic neuropathy or corneal exposure. Headache can also be a presenting feature, particularly relevant to neurologists encountering TED in a general headache or diplopia workup.¹

Exam Findings

• Eyelid retraction (increased scleral show) and lid lag on downgaze
• Proptosis, measured objectively with exophthalmometry
• Conjunctival injection and chemosis, particularly over the insertions of the horizontal rectus muscles
• Restrictive strabismus pattern on motility exam, often with limited elevation from inferior rectus involvement
• Optic neuropathy signs in severe disease: reduced visual acuity, color vision deficits, relative afferent pupillary defect, and visual field loss, warranting urgent recognition and treatment
• Structured orbital examinations, using tools such as the Clinical Activity Score (assessing pain, redness, swelling) and the EUGOGO (European Group on Graves' Orbitopathy) severity/activity categories, are used to stage disease and guide management decisions¹

Differential Diagnosis

• Orbital cellulitis or other inflammatory orbital disease (distinguished by clinical course, systemic infection signs, and thyroid function testing)
• Orbital mass lesion (lymphoma, metastasis) causing unilateral proptosis, particularly important to exclude in asymmetric or atypical presentations
• Myasthenia gravis (can cause diplopia and ptosis but lacks the restrictive motility pattern and orbital congestive signs of TED)
• Idiopathic orbital inflammation (orbital pseudotumor), distinguished by different imaging characteristics and typically normal thyroid function

Management

Staging activity (Clinical Activity Score) and severity (EUGOGO categories) guides the treatment approach.¹ Key foundational steps for all patients include restoring and maintaining euthyroidism, smoking cessation, and structured, serial orbital examinations to monitor for progression.¹ Urgent cases with vision loss from dysthyroid optic neuropathy require high-dose intravenous glucocorticoids and early orbital decompression surgery to relieve apical compression on the optic nerve — a sight-threatening emergency requiring prompt recognition and action.¹ In active, non-sight-threatening but still inflammatory disease, intravenous methylprednisolone combined with immunosuppressants such as mycophenolate is a preferred approach.¹

Teprotumumab, an insulin-like growth factor-1 receptor (IGF-1R) antagonist, is the first FDA-approved targeted therapy specifically for TED, effective for reducing proptosis and inflammation.² However, increasing post-marketing evidence has linked teprotumumab to auditory adverse events, a biologically plausible effect given that IGF-1 signaling is essential for cochlear maintenance and neuroprotection, meaning systemic IGF-1R inhibition can affect the ear as well as the orbit.² Reported auditory effects most commonly include bilateral high-frequency sensorineural hearing loss, tinnitus, and aural fullness, typically emerging after three to six infusions, with many cases showing persistent deficits despite drug discontinuation; however, no standardized approach to audiologic assessment or monitoring currently exists for patients receiving teprotumumab, and baseline audiometric assessment and monitoring protocols have varied considerably across published studies.² Neurologists, alongside ophthalmologists and endocrinologists, play a vital role in multidisciplinary TED care, including monitoring and patient support throughout treatment.¹

Complications

• Dysthyroid optic neuropathy, the most vision-threatening complication, requiring urgent high-dose glucocorticoids and, often, orbital decompression
• Corneal exposure and ulceration from severe proptosis and lagophthalmos
• Persistent diplopia from restrictive strabismus, sometimes requiring strabismus surgery once disease activity has stabilized
• Teprotumumab-associated ototoxicity (sensorineural hearing loss, tinnitus, aural fullness), which may be persistent despite drug discontinuation and currently lacks standardized monitoring protocols²
• Psychosocial and cosmetic impact from proptosis and lid retraction, an underappreciated but clinically significant aspect of the disease burden

Clinical Pearls

• Restoring euthyroidism and smoking cessation are foundational management steps for every TED patient, regardless of ocular disease severity¹
• Vision loss from dysthyroid optic neuropathy is a sight-threatening emergency requiring urgent high-dose IV glucocorticoids and early orbital decompression¹
• Structured staging with the Clinical Activity Score and EUGOGO categories should guide, not just describe, the treatment approach¹
• Teprotumumab is an effective, FDA-approved targeted therapy for TED, but carries an increasingly recognized, potentially irreversible risk of ototoxicity that warrants proactive patient counseling²
• No standardized audiologic monitoring protocol yet exists for teprotumumab; clinicians should maintain a high index of suspicion for hearing changes during treatment given inconsistent current surveillance practices²

Common Pitfalls

• Delaying recognition of dysthyroid optic neuropathy, missing the window for urgent, vision-preserving treatment
• Overlooking smoking cessation and thyroid function optimization as foundational, non-negotiable early management steps
• Prescribing teprotumumab without counseling patients on the possibility of auditory adverse effects or arranging any baseline/follow-up hearing assessment
• Attributing diplopia in a TED patient solely to myasthenia gravis or another neuromuscular cause without considering the restrictive motility pattern characteristic of TED
• Failing to involve a multidisciplinary team (ophthalmology, endocrinology, and, where relevant, neurology) in managing a condition that frequently spans specialties