April 23, 2015: Pseudo-internuclear Ophthalmoplegia
April 23, 2015
Internuclear ophthalmoplegia, known as an ‘INO’, is an eye movement disorder of conjugate lateral gaze. In an INO, there is absence of adduction of one eye with dissociated nystagmus observed in the contralateral, abducting eye. Lesions causing an internuclear ophthalmoplegia are located in the heavily myelinated tract of the medial longitudinal fasciculus (MLF), commonly ipsilateral to the abnormal adducting eye. Anatomically, the medial longitudinal fasciculus connects the ipsilateral abducens nucleus to the contralateral oculomotor nucleus to result in conjugate lateral gaze. Leading etiologies include ischemia and demyelination to this pontine region. In pseudo-internuclear ophthalmoplegia, there is often an observed bilateral INO, raising concern for demyelinating disease. In addition, abnormal convergence is frequently seen. When imaging is normal, this raises the suspicion on a pseudo-INO. Such findings can be observed in patients with diagnosed or unrecognized myasthenia gravis and is felt to be secondary to abnormal neuromuscular transmission, rather than a central nervous system lesion.
- Yamazaki Y, Sugiura T, Kurokawa K. Pseudo-Internuclear Ophthalmoplegia as a Sign of Overlapping Myasthenia Gravis in a Patient with ‘Intractable’ Hypothyroidism. Inter Med 2010; 49: 69-72.
Submitted by James Addington, M.D. Resident Physician, Department of Neurology, University of Virginia
Disclosures: Dr. Addington is a member of the Residents & Fellows Section of Neurology.