Case Report: Intracranial hypertension occurring in association with subacute thyroiditis

Subacute thyroiditis (SAT) is a self-limited inflammatory thyroid disorder that typically produces a transient thyrotoxic phase. Intracranial hypertension (IH) is a rare but potentially sight-threatening complication of thyrotoxicosis, reported almost exclusively in hyperthyroidism, with only a single previous report linking it to SAT. We report the case of a 29-year-old woman who developed IH during the thyrotoxic phase of subacute thyroiditis, temporally related to dental manipulation. She presented with headache, nausea, vomiting, and fever, followed by a syncopal episode; clinical, laboratory, and imaging findings led to a diagnosis of subacute thyroiditis with overt thyrotoxicosis. She later developed bilateral visual blurring and pulsatile tinnitus, and ophthalmological evaluation showed bilateral papilledema with reduced visual acuity (20/100 right eye, 20/33 left eye) and visual field defects. Lumbar puncture demonstrated an opening pressure of 47.6 cmH₂O (35 mmHg) with normal cerebrospinal fluid composition; neuroimaging did not document venous sinus thrombosis or structural lesions. She was started on acetazolamide and corticosteroids, with subsequent recovery of visual acuity, although an inferior visual field defect persisted in the right eye. This is the second reported case of IH associated with subacute thyroiditis. This case underscores that fundus examination should be performed in every patient with a new or unexplained headache, since papilledema may cause irreversible optic nerve damage before visual symptoms appear, and that early treatment with acetazolamide, together with management of the underlying thyroid disorder, can prevent permanent visual loss.