Hemi see-saw nystagmus

This is a case report of a rare form of see-saw nystagmus, hemi see-saw nystagmus (HSSN), characterised by a lesion near Cajal’s interstitial nucleus. Few cases have been reported since Maddox’s original description in 1913 (for a review see Leigh and Zee, 1999).

A 32 year-old woman presented with oscillopsia of sudden onset. Three years earlier she had surgery for a pilocytic astrocytoma of the pons. Examination two days after onset showed cyclic binocular movements: depression-extorsion of the left eye with synchronous elevation-intorsion of the right, followed by and alternating with a reversed cycle. The nystagmus contained both slow and rapid movements. Between cycles of nystagmus right hypotropia and left hypertropia indicative of skew deviation were noted. The ophthalmological and neurological examinations were otherwise normal. A FLAIR T2-weighted MRI scan showed increased signal near Cajal’s interstitial nucleus on the left.

Clonazepam 1mg /day resulted in complete recovery of visual symptoms and of the nystagmus by 2 months.

The authors discuss the pathophysiology of the condition and conclude that HSSN results in a lesion of the vestibular-ocular pathways in the vicinity of Cajal’s nucleus.

5 references.