Longitudinal Study of Timed 25 Foot Walks and Rnfl in a Large MS Cohort

Background: Correlation between anatomical parameters with measurements of clinical function is needed in order to validate them as surrogate markers and establish practical implications for patient management in MS.   Measurement of the retinal nerve fiber layer (RNFL) by Optical Coherence Tomography (OCT) is a reliable, non-invasive quantification of a neuronal compartment that correlates with brain volume loss as measured by MRI.  The timed 25 foot walk (T25FW) is a simple bedside test that correlates well with other measures of walking ability and has been identified as having a relationship with functional level and disease progression.                               

Objectives: Identify if RNFL measurement correlates with T25FW and serves as a surrogate anatomical marker of functional decline in individuals with Multiple Sclerosis (MS).                                                 

Methods: This was a longitudinal study of 514 MS patients with mean age of 48.0 (± .54). The sample consisted of 408 females and 106 males. Mean disease duration was 9.8 years ±.26; 89% were on disease modifying therapies.  Each subject had OCT and T25FW measured at two time-points, separated by 1 to 3 years. 

Results: Spearman rho correlation was used to look at the relationship between RNFL and T25FW at the two points.  While both correlations proved significant (time 1: rho = -.10, p = .02; time 2: rho = -.12, p = .007), the magnitudes were very small. Further, the correlation between the changes in RNFL and changes in T25FW was not significant (r=-.02, p = 0.69). These results indicate that RNFL and T25FW are only trivially correlated. 

Conclusions: Current study examined the relationship between RNFL and T25FW over a span of up to three years in a large cohort. A significant relationship was found, but the effect was very small. As functional decline in MS can happen at a slow rate, the study will be continued longitudinally.