Cause of acquired onset of diplopia due to isolated third, fourth, and sixth cranial nerve palsies in patients aged 20 to 50 years in Korea: A high resolution magnetic resonance imaging study

Aims: This study aimed to describe the etiologies of acquired onset of diplopia due to isolated third, fourth, and sixth cranial nerve palsies in young adults in Korea. Methods: This retrospective study included 127 patients aged 20 to 50 years with acquired onset isolated third, fourth, and sixth cranial nerve palsies who received care at the Strabismus and Neuro-ophthalmology Department of Samsung Medical Center from 2013 to 2017. The etiologies of the palsies determined by clinical assessment, high-resolution magnetic resonance imaging (MRI) with three-dimensional constructive interference in steady state, and laboratory testing were analyzed. Results: Fifty-nine patients manifested sixth cranial nerve palsy. Forty-six patients had fourth cranial nerve palsy and 22 patients had third cranial nerve palsy. The most common etiologies of the ocular motor nerve palsies were presumed inflammatory lesions (21.3%), followed by presumed microvascular causes (17.3%), and neoplasms involving the central nervous system (15.7%). Neoplasms were the most common cause of sixth cranial nerve palsy (25.4%). The most common cause of fourth cranial nerve palsy was presumed microvascular ischemia (28.3%), and presumed inflammatory lesions was the most common cause of third cranial nerve palsy (36.4%). Other non-traumatic causes included vascular lesions, ischemic brainstem stroke, intracranial hemorrhage, non-aneurysmal neuro-vascular contact, multiple sclerosis, and infection. Conclusion: A substantial proportion of young adult patients with ocular motor nerve palsies manifested pathologies other than presumed microvascular ischemia or idiopathic causes. Neuroimaging and laboratory tests have important roles in the evaluation of patients aged 20-50 years with acquired ocular motor nerve palsies.