A 25-Year-Old Woman With a Droopy Eyelid and Double Vision

Monica Saini, MD, MBBS

Disclosures

March 20, 2020

RPON is a rare disorder and has been reported in patients aged 7 months to 50 years. In most patients, headache occurs around 1.5 days on average before ophthalmoplegia; however, in 25% of patients, episodes may be painless.[4] Headache in RPON is thought to be secondary to irritation of sensory pain fibers of the trigeminal nerve traversing the third cranial nerve, triggering a trigeminovascular response. Complete third nerve palsy with pupil involvement is the most common presentation; however, partial involvement may occur. The involvement of multiple oculomotor nerves is seen in < 10% of cases. Headache may last a few days to a week, and ophthalmoplegia may persist for 2-3 weeks to 2-3 months.[5] Recovery from an attack of RPON may not be complete, especially after multiple episodes.[6]

Enhancement of the oculomotor nerve is seen in most patients, usually at the nerve root exit zone in the interpeduncular cistern.[5] MRI abnormalities usually resolve after the episode (< 3 months), but resolution may take months to years; typically, enhancement resolves before improvement in thickening is noted.

The pathogenesis of RPON has not yet been determined. Theories include microvascular ischemia secondary to vasa nervosum compromise, release of inflammatory neuropeptides, vasospasm related to blood-neural barrier damage, and structural compromise by vascular anomalies that increase susceptibility of the cranial nerve to an altered trigeminovascular response.[7,8,9]

The differential diagnoses of a painful third nerve palsy includes aneurysm, most commonly involving the posterior communicating artery, Tolosa-Hunt syndrome, vasculitic and nonvasculitic arteritic cranial neuropathy, meningeal infiltrative disorders, carotid-cavernous fistula, arterial dissection, cavernous sinus pathologies, and mass lesions.

Tolosa-Hunt syndrome presents with periorbital headache and cranial nerve palsy, both of which show excellent response to corticosteroids. Neuroimaging easily differentiates Tolosa-Hunt syndrome from RPON, with evidence of granulomatous inflammation seen in the orbit, superior orbital fissure, and/or the cavernous sinus.[10]

Arteritic cranial neuropathy, typically oculomotor neuropathy in patients with diabetes, tends to be painless and is more commonly seen in older individuals with clear vascular risk factors. Giant cell arteritis (GCA) must be considered in patients older than 50 years. A history of systemic symptoms (eg, fever, weight loss), jaw claudication, and arthritis must be present and temporal artery tenderness or loss of pulsatility must also be reported. Evaluation of inflammatory markers, including erythrocyte sedimentation rate and C-reactive protein level, and fundus examination is mandatory in patients with features suggestive of GCA. Depending on associated systemic and neurologic features, investigations for painful third nerve palsy may include spinal fluid examination and meningeal biopsy.

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