In the right clinical context, decreased visual acuity + papilledema = BAD. These patients need workup including LP and MRI in the ED, and urgent referral to ophthalmology (for optic nerve sheath fenestration) or neurosurgery (for shunt placement).
Papilledema can be difficult to recognize. Beware of mimics such as optic nerve head drusen and decreased optic disc height.
LP is essential in the workup of IIH, but is limited by many potential confounders. To maximize accuracy in obtaining an opening pressure reading, remember la clé (French for "the KEY")- Calm patient, Lateral decubitus position, knees Extended