Isolated bilateral horizontal gaze palsy as first manifestation of multiple sclerosis

Predilection sites for infratentorial multiple sclerosis lesions are well known and frequently involve the fasciculus longitudinalis medialis leading to classical internuclear ophthalmoplegia. We report a very rare oculomotor disorder due to a demyelinating central nervous system (CNS) lesion in the medial part of the lower pontine tegmentum. A 36-year-old man presented with sudden onset of blurred vision. Clinically there was limited eye adduction and abduction to either side, which corresponds to bilateral horizontal gaze palsy. Brain magnetic resonance imaging (MRI) showed a demyelinating CNS lesion affecting the fasciculus longitudinalis medialis, abducens nuclei or abducens fibres in the medial part of the lower pontine tegmentum. Furthermore there were six further demyelinating white matter lesions fulfilling all Barkhof criteria for multiple sclerosis. Demyelinating CNS lesions causing isolated bilateral horizontal gaze palsy are exceptional and usually associated with further focal neurological deficits, which was not the case in the presenting patient. This is a unique video report of isolated bilateral horizontal gaze palsy as the initial manifestation of demyelinating CNS disease, which lead to definite diagnosis of relapsing remitting multiple sclerosis.