Background: In vitro studies of Miller Fisher syndrome (MFS) have demonstrated anti-GQ1b IgG antibodymediated presynaptic damage at the neuromuscular junction. Previous studies have provided electrophysiological evidence of presynaptic neuromuscular transmission defect in MFS in anti-GQ1b positive patients, which persisted up to 3 months from initial presentation. Methods and results: In this study, we show that incremental responses were significantly greater in antibodypositive MFS and Bickerstaff's brainstem encephalitis, compared with antibody-negative Guillain-Barre and MFS variants. These responses return to normality by 6 months, in tandem with clinical recovery. Conclusions: The findings have pertinent implications on developing management strategies of these conditions.