Postural Body Sway as Surrogate Outcome for Myelopathy in Adrenoleukodystrophy

Abstract

Background: Myelopathy is the core clinical manifestation of adrenoleukodystrophy (ALD), which is the most common peroxisomal disorder. Development of therapies requires sensitive and clinically relevant outcome measures. Together with spastic paraparesis, balance disturbance is the main cause of disability from myelopathy in ALD. In this cross-sectional study, we evaluated whether postural body sway - a measure of balance - could serve as a surrogate outcome in clinical trials.

Methods: Forty-eight male ALD patients and 49 age-matched healthy male controls were included in this study. We compared sway amplitude and sway path of ALD patients to controls. We then correlated the body sway parameters showing the largest between-group differences with clinical measures of severity of myelopathy. To correct for age, we performed multiple linear regression analysis with age and severity of myelopathy as independent variables.

Results: All body sway parameters were significantly higher in patients than in controls, with medium to large effect sizes (r = 0.43-0.66, p < 0.001). In the subgroup of asymptomatic patients, body sway amplitude was also higher, but the difference with controls was smaller than for symptomatic patients (effect size r = 0.38-0.46). We found moderate to strong correlations between body sway amplitude and clinical severity of myelopathy (r = 0.40-0.79, p < 0.005). After correction for age, severity of myelopathy was a significant predictor of body sway amplitude in all regression models.

Conclusions: These results indicate that postural body sway may serve as a surrogate outcome for myelopathy in ALD. Such outcomes are important to evaluate new therapies in clinical trials. Further longitudinal studies are needed and ongoing in this cohort.

Keywords: X-linked adrenoleukodystrophy; balance; body sway; myelopathy; spinal cord; surrogate outcome.

FIGURE 1

Study overview. (A) Experimental setup. Upper panel: subject standing on the force plate in the feet-apart condition. Lower panel: body sway output. The body sway amplitude is the displacement of the center of gravity in the anteroposterior (y-axis) or mediolateral (x-axis) direction, the sway path is the distance traveled by the blue line. (B) Differences in body sway amplitude between patients and controls (left) and asymptomatic patients and an age-matched selection of controls (right). (C) Two examples of the association between clinical severity of myelopathy and body sway: EDSS and total sway amplitude (left) and 6MWT and total sway amplitude (right). The lines represent simple linear regression lines.

FIGURE 2

Scatter plot of the association between age and total sway amplitude for both patients (red) and controls (blue). The lines represent simple linear regression lines.