Background
Microcystic macular edema (MME) of the retinal inner nuclear layer (INL) has recently been identified in multiple sclerosis (MS) patients with optical coherence tomography (OCT). We aimed to determine if MME of the INL, and/or higher thickness of the INL, are associated with disease activity, or disability progression.
Methods
This retrospective study was performed at Johns Hopkins Hospital (between 09/2008 and 03/2012). 164 MS patients and 60 healthy-controls underwent serial OCT scans and clinical evaluation (including visual function). OCT scanning, including automated intra-retinal layer segmentation, yielded thicknesses of the retinal nerve fiber layer, ganglion cell layer (plus inner plexiform layer), INL (plus outer plexiform layer), and outer nuclear layer. MS patients also underwent annual brain MRI scans. Disability scores were compared with the Wilcoxon rank-sum test. Mixed-effects linear regression was used to compare OCT measures and letter-acuity scores. Logistic regression was used to examine the relationships of baseline OCT thicknesses with clinico-radiological parameters.
Findings
Mean follow-up (standard deviation) for MS patients and healthy-controls was 25路8-months (9路1-months) and 22路4-months (11路4-months) respectively. 10 MS patients (6路1% of the cohort) demonstrated MME during at least one study visit, but MME was not visible at baseline in 6 of these patients. MS patients with vs. without MME (151 MS patients) at any time during the study had higher baseline multiple sclerosis severity scores (p=0路032), although expanded disability status scale (EDSS) scores were not significantly different (p=0路097). MS eyes with MME (12 eyes) vs. without MME (302 eyes) had lower letter-acuity scores (100%-contrast: p=0路017; 2路5%-contrast: p=0路031; 1路25%-contrast: p=0路014), and higher INL thicknesses (p=0路003) at baseline. Higher baseline INL thickness in MS predicted the development of contrast-enhancing lesions (p=0路007), new T2 lesions (p=0路015), EDSS progression (p=0路034), and relapses (in relapsing-remitting MS; p=0路008) during the study. MME was not associated with disease activity during follow-up. Healthy-controls did not demonstrate MME.
Interpretation
Increased INL thickness on OCT, potentially representing inflammation of the unmyelinated retina, is associated with disease activity in MS. If this finding is confirmed, INL thickness may be a useful predictor of disease progression in MS.
Funding
National Multiple Sclerosis Society (TR3760-A-3, RG4212-A-4), National Eye Institute (R01-EY014993, R01-EY019473), Braxton Debbie Angela Dillon and Skip Donor Fund.