Looking Beyond the Midline: An Uncommon Etiology of Internuclear Ophthalmoplegia of Abduction Due to Cerebral Venous Thrombosis.

Abstract

Introduction: Internuclear ophthalmoplegia (INO) is a horizontal gaze disorder caused by medial longitudinal fasciculus lesions. INO of abduction is an exceptionally rare variant characterized by abduction limitation with preserved convergence and contralateral adduction nystagmus, with unclear pathophysiology, and only a limited number of cases have been reported.

Case report: A 27-year-old man presented with headache, vomiting, seizures, and altered sensorium. Examination revealed bilateral disc edema and abduction restriction of the right eye, with contralateral adduction nystagmus, consistent with INO of abduction. Brain MRI showed no brainstem lesions, while MR venography demonstrated cerebral venous thrombosis of the superior sagittal, left transverse, and sigmoid sinuses. Vitamin B12 deficiency with hyperhomocysteinemia was detected. Treatment with anticoagulation and acetazolamide resulted in complete resolution of the ocular motility deficits.

Conclusion: This case highlights a reversible form of INO of abduction associated with raised intracranial pressure in the absence of structural brainstem lesions, likely due to pressure-mediated disruption of inhibitory gaze pathways. INO of abduction is an ultrarare but clinically important sign. Its recognition in patients with intracranial hypertension and normal brainstem imaging may aid in localization and facilitate timely, reversible treatment.