Isolated sixth-nerve palsy as the presenting sign of multiple sclerosis

Abstract

The author reports a young patient presenting isolated (fascicular) abducens nerve palsy as the only and first sign of multiple sclerosis. Whereas diplopia-a common symptom of multiple sclerosis-is usually due to supranuclear brainstem dysfunction, it is rarely caused by sixth-nerve palsy. In larger series analysing the aetiologies of sixth-nerve palsies, multiple sclerosis was a rare cause, particularly in the case of isolated sixth-nerve palsy. However, these studies were done decades ago when adequate imaging procedures were not available. Nowadays, the large group with undetermined cause should shrink when appropriate diagnostic work-up such as application of MRI is performed. This case demonstrates that demyelinating brainstem lesions with appropriate location in the course of the sixth-nerve fascicle may cause isolated sixth-nerve palsy.