Compressive Optic neuropathy secondary to Thyroid Eye Disease.
Thyroid associated ophthalmopathy (TAO) is potentially a sight threatening disease occurring with or without thyrotoxicosis.† Most common features of hyperthyroidism are lid lag and lid retraction but TAO will also be associated with chemosis, proptosis and external ophthalmoplegia.† The condition has an annual incidence rate of 16 women and 3 men per 100,000 population.† Compressive optic neuropathy is the presenting feature in only 3-5 % of patients.
A 54 year woman developed acute visual loss in the left eye for few hours.† She had a history of thyrotoxicosis associated with Gravesí disease in the past and was treated with hemi-thyroidectomy in Poland. She had presented with relapsed thyrotoxicosis two months previously and was controlled with block and replace therapy.† There was regular ophthalmology review.
She was clinically euthyroid.† The visual acuity was 1/6 in the left eye as compared to 6/6 in the right eye and diplopia in all directions of gaze.† There was limitation in left eye movement to 5 degree abduction and 15 degree elevation/depression in the midline. There was no evident proptosis or exophthalmos.† There was optic disc swelling on the left side. †The central nervous system examination was otherwise normal.
Left eye showed impairment of Ishihara chart reading to 5/17 charts as compared to 17/17 over the normal side. Her TSH was 0.29 mU/L and Free T4 10.2pmol/L.† The thyroid peroxidase antibody level was >1000 IU.† She received 1 gram methyl prednisolone on alternate days as treatment and had alternate days eye acuity assessment. †Magnetic resonance imaging demonstrates modest proptosis and modest apical crowding.† Her vision improved to 6/6 visual acuity after one week of treatment. She is currently being managed with cycles of orbital irradiation.
The prevalence of ophthalmopathy in Gravesí hyperthyroidism depends on the detailsof the assessment.† Patients with very mild cases may have low-grade orbital inflammation with some orbital discomfort, tearing, and chemosis. Other patients may have mild proptosis with or without lid retraction.† More severely there may be marked inflammation, severe discomfort, corneal problems, or optic nerve compression.† Patients may have diplopia with external opthalmoplegia. This case illustrates the importance of prompt diagnosis and management of compressive thyroid ophthalmopathy with limited external features.† Patients with limited external features of Gravesí disease might have significant orbitopathy which may severely compromise vision. Decreased visual acuity might be the earliest sign in patients with thyroid eye disease. Surgical management of orbital pressure is both an alternative and adjunctive treatment to medical therapy, which most often involves corticosteroids, external beam radiotherapy, or both.