Bilateral Internuclear Ophthalmoplegia Reversed by Naloxone

We encountered an apparent bilateral internuclear ophthalmoplegia (INO) in a stuporous patient who used narcotics and benzodiazepines and had taken phenytoin sodium for drug-withdrawal seizures. The INO was promptly reversed by administration of the narcotic antagonist naloxone, which binds opiate receptors. This suggests the INO resulted from a specific toxic effect of narcotics, but opiate receptors have not been anatomically demonstrated within the medial longitudinal fasciculus or associated structures. Stimulation of inhibitory GABA-ergic (α-aminobutyric acid) vestibulo-ocular fibers may have been related to INO in this case.