Internuclear ophthalmoplegia associated with transient torsional nystagmus

The association of internuclear ophthalmoplegia (INO) with torsional nystagmus is rare. We report the case of a 63-year-old man presenting with sudden onset of diplopia. On ocular examination, he had left INO and a torsional nystagmus with counter-clockwise quick-phases from the patient's point of view in the primary position, ipsiversive to the side of the medical longitudinal fasciculus (MLF) lesion at the pontomesencephalic junction on magnetic resonance images. Neither skew deviation nor head tilting was noted at that time. Two days later, the torsional nystagmus disappeared, although the limitation of adduction in the left eye remained. We speculate that with sparing of the rostral interstitial nucleus of the MLF, a small lesion in the MLF may involve the ipsilateral vertical integrator, the interstitial nucleus of Cajal, producing an INO associated with a transient ipsiversive torsional nystagmus.