Third nerve palsy
Third nerve palsy is dysfunction of the oculomotor nerve producing ptosis, a down-and-out eye, and often a dilated pupil; a non-pupil-sparing or painful presentation is a posterior communicating artery aneurysm until emergent CT or MR angiography and neurosurgical evaluation prove otherwise, while pupil-sparing cases are managed with vascular risk-factor control.
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What this article covers
- Overview
Third nerve palsy is dysfunction of the oculomotor nerve (cranial nerve III), which supplies the medial, superior, and inferior recti, the inferior oblique, the levator palpebrae superioris, and…
- Epidemiology
Third nerve palsy most often affects older adults with vascular risk factors: long-standing diabetes mellitus and hypertension are the leading associations, and microvascular disease raises the risk…
- Risk factors
Diabetes mellitus: the leading vasculopathic risk factor for ischemic, pupil-sparing palsy through microvascular compromise of the nerve's blood supply.
- Pathophysiology
The oculomotor nucleus sits in the midbrain at the level of the superior colliculus; its fascicles cross the midbrain tegmentum, the nerve exits ventrally, crosses the subarachnoid space beneath the…
- Clinical features
Ptosis: partial to complete eyelid closure from loss of levator tone; patients often lift the lid manually to see.
- Differential diagnosis
Cavernous sinus syndrome (thrombosis or mass lesion): adds impairment of cranial nerve IV, VI, V1/V2, or oculosympathetic fibers, and often proptosis, none of which occur in an isolated palsy.
- Diagnosis
What establishes the diagnosis: the diagnosis is made clinically from ptosis, a down-and-out resting eye position, and impaired adduction, elevation, and depression with preserved abduction; the…
- Management
First, triage by pupil status and pain: any new non-pupil-sparing or painful palsy is a neurosurgical emergency; obtain CT or MR angiography immediately and admit for neurosurgical evaluation.
- Complications
Subarachnoid hemorrhage: the feared consequence of a missed aneurysm, carrying high mortality if it ruptures before it is secured.
- Prognosis
Ischemic, pupil-sparing palsy typically follows a self-limited course, improving within 6-12 weeks and largely resolving over the following months once vascular risk factors are addressed; recurrence…
- Prevention
Vascular risk-factor control: keep blood pressure below 130/80 mmHg and hemoglobin A1c below 7% to reduce ischemic mononeuropathy and its recurrence.
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