A case report and review: oculomotor nerve palsy associated with diabetes mellitus

Background: A longstanding clinical dictum maintains that oculomotor nerve mononeuropathy with pupil sparing is most likely secondary to an ischemic vasculopathy, while oculomotor nerve mononeuropathy with pupillary involvement is considered to be secondary to a subarachnoid aneurysm until proven otherwise. Notably, this dictum fails to accurately predict etiology in a significant number of cases of oculomotor palsy, as many diabetics suffer ischemic oculomotor palsy characterized by initial pupillary dysfunction. A case report is presented describing a 62-year-old female diabetic patient taking hormone supplements who developed an acute right third nerve palsy with partial pupillary involvement and periorbital eye pain. Although an ischemic etiology was suspected, magnetic resonance imaging and cerebral angiography were performed to rule out an aneurysmal etiology. Neuro-radiologic testing revealed no intracranial pathology, suggesting an isolated, self-limited, microvascular etiology of the oculomotor palsy. The mononeuropathy gradually resolved over the next eight weeks. Conclusions: This case demonstrates that ischemic oculomotor palsy may present with pupillary dysfunction, contradicting the clinical dictum maintaining that spared pupils are associated with ischemia and affected pupils are associated with aneurysm in acute, isolated oculomotor palsy. The discussion section covers isolated oculomotor palsy and its related pupillary postures and offers possible pathophysiologic explanations for the various relationships.