Downward gaze palsy caused by bilateral lesions of the rostral mesencephalon

A 55-year-old man with diabetes mellitus developed diplopia and experienced difficulty in moving his eyes in the vertical plane, especially downward. Horizontal movement of each eye was normal with exotropia. Magnetic resonance imaging revealed small and high signals on both sides of the midbrain near the interstitial nucleus of Cajal (INC). Based upon the recent experimental evidence, we speculate that bilateral lesions involving the INC may have caused downward gaze palsy in our patient.