Use of Corneal Confocal Microscopy to Detect Corneal Nerve Loss and Increased Dendritic Cells in Patients With Multiple Sclerosis

IMPORTANCE Multiple sclerosis (MS) is characterized by demyelination, axonal degeneration, and inflammation. Corneal confocal microscopy has been used to identify axonal degeneration in several peripheral neuropathies. OBJECTIVE To assess corneal subbasal nerve plexus morphologic features, corneal dendritic cell (DC) density, and peripapillary retinal nerve fiber layer (RNFL) thickness in patients with MS. DESIGN, SETTING, AND PARTICIPANTS This single-center, cross-sectional comparative study was conducted at a tertiary referral university hospital between May 27, 2016, and January 30, 2017. Fifty-seven consecutive patients with relapsing-remittingMS and 30 healthy, age-matched control participants were enrolled in the study. Corneal subbasal nerve plexus measures and DC density were quantified in images acquired with the laser scanning in vivo corneal confocal microscope, and peripapillary RNFL thickness was measured with spectral-domain optical coherence tomography. MAIN OUTCOMES AND MEASURES Corneal nerve fiber density, nerve branch density, nerve fiber length, DC density, peripapillary RNFL thickness, and association with the severity of neurologic disability as assessed by the Kurtzke Expanded Disability Status Scale (score range, 0-10; higher scores indicate greater disability) and Multiple Sclerosis Severity Score (score range, 0.01-9.99; higher scores indicate greater severity). RESULTS Of the 57 participants with MS, 42 (74%) were female and the mean (SD) age was 35.4 (8.9) years; of the 30 healthy controls, 19 (63%) were female and the mean (SD) age was 34.8 (10.2) years. Corneal nerve fiber density (mean [SE] difference, -6.78 [2.14] fibers/mm(2); 95% CI, -11.04 to -2.52; P =.002), nerve branch density (mean [SE] difference, -17.94 [5.45] branches/mm(2); 95% CI, -28.77 to -7.10; P =.001), nerve fiber length (mean [SE] difference, -3.03 [0.89] mm/mm(2); 95% CI, -4.81 to -1.25; P =.001), and the mean peripapillary RNFL thickness (mean [SE] difference, -17.06 [3.14] mu m; 95% CI, -23.29 to -10.82; P <.001) were reduced in patients with MS compared with healthy controls. The DC density was increased (median [interquartile range], 27.7 [12.4-66.8] vs 17.3 [0-28.2] cells/mm(2); P =.03), independent of a patient's history of optic neuritis. Nerve fiber density and RNFL thickness showed inverse associations with the Expanded Disability Status Scale (rho = -0.295; P =.03 for nerve fiber density and rho = -0.374; P =.004 for RNFL thickness) and the Multiple Sclerosis Severity Score (R = -0.354; P =.007 for nerve fiber density and R = -0.283; P =.03 for RNFL thickness), whereas other study measures did not. CONCLUSIONS AND RELEVANCE These data suggest that corneal confocal microscopy demonstrates axonal loss and increased DC density in patients with MS. Additional longitudinal studies are needed to confirm the use of corneal confocal microscopy as an imaging biomarker in patients with MS.