Isolated sixth nerve palsy: an uncommon presenting sign of multiple sclerosis.

We describe three patients in whom an isolated sixth nerve palsy was the only clinical symptom or sign of multiple sclerosis (MS). Data were collected prospectively over 6 years on these three patients, who showed no other signs of brainstem dysfunction or prior symptoms; in addition. Retrospective analysis of all patients with MS and all patients with sixth nerve palsy referred to a neuro-ophthalmology service between 1982 and 1998 showed isolated sixth nerve palsy to be the presenting sign of MS in only 0.5% of these patients. MS was the cause of isolated sixth nerve palsy in 0.8% of all patients and in 1.6% of those aged 18-50 years. Although it has been previously suggested that sixth nerve palsy is a not uncommon presenting sign of MS, our results suggest it is rare.