Background Current findings suggest that eye movement abnormalities in ALS relate to frontal lobe impairment. Numerous case reports, however, describe slow saccades and supranuclear gaze palsies in patients with MND often associated with bulbar-onset disease. We performed a study of reflexive horizontal saccades and ocular fixation in patients with MND to examine for any differences between bulbar-onset, spinal-onset ALS and controls. We then compared the results for bulbar-onset ALS with a group of patients with PSP.

Methods Forty-four ALS patients, 45 controls and seven PSP patients were included in the study. Reflexive horizontal saccades (latency and speed) and ocular fixation (saccadic intrusion amplitude, frequency and fixation period) were examined using infrared oculography and all subjects then underwent neuropsychological evaluation.

Results Saccades were found to be slower in bulbar-onset compared to spinal-onset patients and controls (p=0.03, p=0.05). No statistically significant difference in saccade speed was observed between bulbar-onset ALS and PSP patients. PSP patients, however, had larger saccadic intrusions compared to bulbar-onset ALS patients.

Conclusions This is the first study to highlight the presence of slow saccades in bulbar-onset MND. It is likely that a spectrum exists, ranging from normal saccade speed to the presence of a gaze palsy. These observations highlight the potential for diagnostic confusion between bulbar-onset MND and PSP.