Incidence and Etiologies of Acquired Third Nerve Palsy Using a Population-Based Method

Abstract

IMPORTANCE Among cranial nerve palsies, a third nerve palsy is important because a subset is caused by life-threatening aneurysms. However, there is significant disagreement regarding its incidence and the reported etiologies.OBJECTIVE To determine the incidence and etiologies of acquired third nerve palsy using a population-based method.DESIGN, SETTING, AND PARTICIPANTS All newly diagnosed cases of acquired third nerve palsy from January 1, 1978, through December 31, 2014, in Olmsted County, Minnesota, were identified using the Rochester Epidemiology Project, a record-linkage system of medical records for all patient-physician encounters among Olmsted County residents. All medical records were reviewed to confirm a diagnosis of acquired third nerve palsy and determine the etiologies, presenting signs, and symptoms. Incidence rates were adjusted to the age and sex distribution of the 2010 US white population. MAIN OUTCOMES AND MEASURESIncidence and etiologies of acquired third nerve palsies. The secondary outcome was incidence of pupil involvement in acquired third nerve palsies. RESULTSWe identified 145 newly diagnosed cases of acquired third nerve palsy in Olmsted County, Minnesota, over the 37-year period. The age-and sex-adjusted annual incidence of acquired third nerve palsy was 4.0 per 100 000 (95% CI, 3.3-4.7 per 100 000). The annual incidence in patients older than 60 was greater than patients younger than 60 (12.5 vs 1.7 per 100 000; difference, 10.8 per 100 000; 95% CI, 4.7-16.9; P < .001). The most common causes of acquired third nerve palsy were presumed microvascular (42%), trauma (12%), compression from neoplasm (11%), postneurosurgery (10%), and compression from aneurysm (6%). Ten patients (17%) with microvascular third nerve palsies had pupil involvement, while pupil involvement was seen in 16 patients (64%) with compressive third nerve palsies. CONCLUSIONS AND RELEVANCEThis population-based cohort demonstrates a higher incidence of presumed microvascular third nerve palsies and a lower incidence of aneurysmal compression than previously reported in non-population-based studies. While compressive lesions had a higher likelihood of pupil involvement, pupil involvement did not exclude microvascular third nerve palsy and lack of pupil involvement did not rule out compressive third nerve palsy.

Clinical Reasoning: Headaches and double vision in a 68-year-old woman

“…Microvascular third nerve palsy, due to undiagnosed hypertension or diabetes mellitus, was also considered as it is the most common cause of oculomotor nerve palsy. 2 Head CT and follow-up MRI demonstrated a right-sided, homogenously enhancing extraaxial frontotemporal mass with minimal associated right-to-left midline shift. A CSF cleft was visible around the margins of the lesion and there was no evidence of nearby sulcal effacement (figure, A).…”

“…1 In addition, the presence of a partial third nerve palsy, even if pupil sparing, requires imaging to evaluate for the presence of a posterior communicating artery aneurysm. 2 Apart from an aneurysm, though the list of intracranial lesions that could potentially cause the patient's presentation is extensive, more likely etiologies included an extra-axial lesion along the medial sphenoid wing, anterior clinoid, or within the cavernous sinus. Microvascular third nerve palsy, due to undiagnosed hypertension or diabetes mellitus, was also considered as it is the most common cause of oculomotor nerve palsy.…”

Unequal pupils: Understanding the eye’s aperture

“…Of those patients presenting with an acquired oculomotor palsy, only 6% were found to have compression from an aneurysm and, of these compressive oculomotor nerve palsies, only 64% had pupil involvement. 8 However, all patients with a new-onset oculomotor nerve palsy should be presumed to have a posterior communicating artery aneurysm until proven otherwise, meaning they require urgent neuroimaging. Conversely, failure of dilation is most obvious in the dark.…”

A 51-year-old woman with binocular diplopia and unilateral ptosis

“…Isolated, pupil-sparing oculomotor nerve palsy is most often due to a microvascular cause, whereas isolated pupil-involving oculomotor nerve palsy is most commonly due to compression from an aneurysm or tumor. 1 Because of the potential for imminent subarachnoid hemorrhage caused by an intracerebral aneurysm, emergent imaging (magnetic resonance angiogram or CTA) is warranted in cases of oculomotor nerve palsy with partial or complete pupil involvement. While our patient's pupil was dilated, the pupillary light reflex was diminished but not absent.…”