When one eye tells the whole story: a rare case of unilateral papilledema from IIH

A 35-year-old woman with an elevated BMI was referred for neuro-ophthalmology after her optometrist spotted swelling of the left optic disc. She'd been experiencing left-sided retro-orbital pain, transient vision loss when bending over, and intermittent pulsatile tinnitus for about a year — classic red flags for elevated intracranial pressure. But there was a catch: her papilledema was entirely one-sided, which is atypical for idiopathic intracranial hypertension (IIH) and initially pointed clinicians toward other diagnoses like optic neuritis or a compressive lesion.

After ruling out inflammatory and structural causes via orbital MRI, a lumbar puncture confirmed the diagnosis — her opening pressure was a markedly elevated 34 cm H₂O. She was started on acetazolamide and counseled on weight loss. Within months, her symptoms resolved and her optic disc swelling cleared completely. Four years later, she remains off medication with no recurrence.

Key Takeaways

• Unilateral papilledema, while rare, can be a presentation of IIH — occurring in only ~1.4% of IIH cases
• Preserved visual acuity, color vision, and visual fields in the setting of disc edema should raise suspicion for a benign (non-compressive, non-inflammatory) process
• Orbital MRI with fat saturation and lumbar puncture are essential workup steps when IIH is suspected despite atypical features
• Anatomical differences in optic canal size or perioptic subarachnoid space compartmentalization may explain why papilledema can be asymmetric or unilateral

Why it matters: This case is a reminder that rare presentations of common diagnoses can be missed if clinicians anchor too early on an atypical feature. IIH should remain on the differential even when papilledema is unilateral — especially in young women with elevated BMI and symptoms of raised intracranial pressure.