Changes in balance function with chronic antiepileptic drug therapy: A twin and sibling study.

Objective: To investigate cross-sectional and longitudinal differences in static and dynamic standing balance measures and lower limb muscle strength in patients who are treated chronically with antiepileptic drugs (AEDs).

Methods: Twenty-six AED exposure-discordant same-gender twin and sibling pairs were studied. Clinical and laboratory balance examinations were conducted twice, separated by at least 1 year. The mean within-pair differences in balance measures were calculated cross-sectionally at baseline and follow-up, and longitudinally.

Results: No significant mean within-pair difference was found at baseline in age (44 years), weight, and height (p > 0.05). Between study assessments, the median (interquartile range [IQR]) interval was 3.0 (2.1-4.3) years in users and 2.9 (2.0-4.4) years in nonusers. The median duration of AED therapy was 19 (11-21) years. At baseline and follow-up, cross-sectional sway measures from posturography (Chattecx Balance System) and clinical static balance tests showed poorer performance in users compared to nonusers on several test conditions (p = 0.002-0.032). At follow-up, the users took longer than nonusers to complete the Four-Square-Step Test (p = 0.005) and Five-Times-Sit-to-Stand Test (p = 0.018). A greater annual rate of deterioration in sway was found in users compared to nonusers using posturography on the anteroposterior tilting platform task with distraction (p = 0.032). In both groups, higher baseline sway predicted greater annual deterioration in sway in all platform conditions (β = 0.3-0.5, p < 0.001-0.013). The annual change in measures did not differ between groups in the clinical balance and lower limb strength assessments.

Significance: In this longitudinal twin and sibling study, chronic AED users had poorer standing balance compared to nonusers. Users showed greater deterioration in postural sway with one dynamic platform condition. AEDs may progressively impair balance mechanisms, although this requires further investigations. Repeated dynamic posturography could provide a basis for preventive trials for maintaining or improving balance.