Optical coherence tomography to measure the progression of myelopathy in adrenoleukodystrophy

Objective: To prospectively determine the value of optical coherence tomography (OCT) as a surrogate outcome measure for the progression of myelopathy in males with adrenoleukodystrophy. Methods: Retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) thickness were measured at baseline, 1- and 2-year follow-up in patients and age-matched controls. We assessed the severity of myelopathy with clinical parameters: Expanded Disability Status Scale (EDSS), Severity Scoring system for Progressive Myelopathy (SSPROM), and timed up-and-go. Linear mixed model analysis was used to compare changes in retinal layer thickness of patients to controls. In addition, we correlated changes in retinal layer thickness with changes in clinical parameters. Results: Longitudinal data were available for 28 patients and 29 controls. Peripapillary RNFL (pRNFL) thickness decreased significantly in patients compared to controls (−1.75µm, p = 0.001), whereas change in macular GCL and RNFL was not different between groups. Analysis of the symptomatic subgroup showed that, apart from a similar decrease in pRNFL thickness, GCL thickness decreased significantly (−0.55 µm, p = 0.014). There were moderately strong correlations between changes in retinal layer thickness and changes in clinical parameters of severity of myelopathy. Interpretation: This prospective study demonstrates the potential of OCT-measured retinal neurodegeneration as a surrogate outcome measure for the progression of myelopathy in adrenoleukodystrophy. As differences were small, our findings need to be confirmed with longer follow-up and/or in a larger patient sample.