Our objective was to create a systematic method when approaching a Cranial Nerve III Palsy in order to reach an accurate diagnosis.

Determining the etiology of a Cranial Nerve III palsy is largely clinician-dependent without a recommended set of guidelines or protocol to follow. 

Through retrospective chart review, this case series discusses three different causes of Cranial Nerve III palsy. The etiologies include a posterior communicating artery aneurysm, ocular myasthenia gravis, and a high-grade optic pathway glioma. 

When evaluating the patient with an oculomotor nerve palsy, the presence or absence of pupil-sparing should be determined first to discern whether the etiology is vascular or compressive in nature. In patients with a pupil-sparing palsy, a vascular workup includes laboratory tests for Hemoglobin A1C, Erythrocyte Sedimentation Rate (ESR), and Complete Blood Count (CBC).  In patients who have a non-pupil-sparing palsy, appropriate imaging such as CT or T2-weighted MRI is used to identify compressive causes. If a clear source for the CN III palsy is not identified after initial workup, further testing is required to evaluate for other etiologies such as myasthenia gravis, botulism, Lyme disease, or ocular myopathies (eg. due to hyperthyroidism or mitochondrial disorders).

Overall, we have identified patterns that can assist in determining common or even rare causes of cranial nerve III palsy, with the hopes to help guide clinicians with their diagnostic workup.