Case Report: Marked bilateral optic disc edema as the presenting manifestation of thyroid eye disease with dysthyroid optic neuropathy.

Purpose: The aim of this study was to report an atypical presentation of dysthyroid optic neuropathy (DON) characterized by severe bilateral optic disc edema mimicking papilledema. Methods: A 71-year-old man with hypothyroidism presented with 6 months of progressive bilateral vision loss and Frisén grade 4-5 optic disc edema. Comprehensive neuro-ophthalmic evaluation, orbital imaging, and laboratory testing were performed to establish the diagnosis. Results: Despite presenting with severe optic disc edema typically associated with papilledema, imaging revealed Type 2 thyroid eye disease with apical muscular crowding exceeding 67% and elevated thyroid-stimulating immunoglobulin. Normal lumbar puncture opening pressure excluded elevated intracranial pressure. Following treatment with high-dose intravenous methylprednisolone and staged bilateral three-wall orbital decompression, visual acuity improved from 20/30 to 20/20 bilaterally, with complete resolution of disc edema and visual field defects at 3 months follow-up. Conclusions: Severe optic disc edema is an uncommon but important presenting feature of DON that may mimic papilledema. This case emphasizes the critical importance of considering thyroid eye disease in the differential diagnosis of bilateral optic disc edema, even in the absence of prominent orbital signs, and demonstrates excellent visual outcomes with prompt corticosteroid therapy and surgical decompression.