Longitudinal Study of Retinal Nerve Fiber Layer Thickness and Macular Volume in Patients With Neuromyelitis Optica; Spectrum Disorder

Neuromyelitis spectrum disorder (NMOSD) is a rare autoimmune disorder previously thought to be a subtype of multiple sclerosis (MS). NMOSD is characterized by episodes of inflammation and damage to astrocytes that primarily results in damage to optic nerve and spinal cord. The objective of this exploratory study was to use optical coherence tomography (OCT) to measure axonal and neuronal health in NMOSD eyes over time.; Nine patients with definite NMOSD were assessed at baseline and follow-up visits (time between visits: 35-55 months). OCT assessment involved a macular volume protocol and a retinal nerve fiber layer (RNFL) thickness scan.; The temporal, inferior, nasal, or superior quadrant and the mean global RNFL thickness, macular thickness, and volume of each NMOSD patient was unchanged compared with baseline for each eye separately and both together. There also was no change between the 2 time points for the OCT measures for eyes affected and unaffected by optic neuritis and all eyes together except for a significant change in the temporal RNFL quadrant when all NMOSD eyes were pooled together (mean = 2.88 μm, SD = 3.7, P = 0.021).; Unlike in MS eyes, ongoing RNFL and macular thinning secondary to brain and optic nerve atrophy could not be observed in NMOSD eyes during an observation period of 4 years. This might be an additional marker to distinguish these 2 diseases. However, to confirm this finding, more long-term data are needed to compare these 2 diseases longitudinally.

Original Contribution Longitudinal Study of Retinal Nerve Fiber Layer Thickness and Macular Volume in Patients With Neuromyelitis Optica Spectrum Disorder Praveena Manogaran, MSc, BSc, Anthony L. Traboulsee, MD, Alex P. Lange, MD Background: Neuromyelitis spectrum disorder (NMOSD) is a rare autoimmune disorder previously thought to be a subtype of multiple sclerosis (MS). NMOSD is characterized by episodes of inflammation and damage to astrocytes that primarily results in damage to optic nerve and spinal cord. The objective of this exploratory study was to use optical coherence tomography (OCT) to measure axonal and neuronal health in NMOSD eyes over time. Methods: Nine patients with definite NMOSD were assessed at baseline and follow-up visits (time between visits: 35-55 months). OCT assessment involved a macular volume protocol and a retinal nerve fiber layer (RNFL) thickness scan. Results: The temporal, inferior, nasal, or superior quadrant and the mean global RNFL thickness, macular thickness, and volume of each NMOSD patient was unchanged compared with baseline for each eye separately and both together. There also was no change between the 2 time points for the OCT measures for eyes affected and unaffected by optic neuritis and all eyes together except for a significant change in the temporal RNFL quadrant when all NMOSD eyes were pooled together (mean = 2.88 mm, SD = 3.7, P = 0.021). Conclusions: Unlike in MS eyes, ongoing RNFL and macular thinning secondary to brain and optic nerve atrophy could not be observed in NMOSD eyes during an observation period of 4 years. This might be an additional marker to distinguish these 2 diseases. However, to confirm this finding, more long-term data are needed to compare these 2 diseases longitudinally. Journal of Neuro-Ophthalmology 2016;36:363-368 doi: 10.1097/WNO.0000000000000404 © 2016 by North American Neuro-Ophthalmology Society Department of Medicine (PM, ALT), University of British Columbia, Vancouver, Canada; Department of Ophthalmology (APL), University of British Columbia, Vancouver, Canada; and Vista Klinik (APL), Binningen, Switzerland. Disclosures of all authors' financial relationships: A. L. Traboulsee has received personal compensation from Chugai, Genzyme, Novartis, Roche, Serono and Teva Innovation for consulting. He has also received research support for principle investigator on clinical trials with Genzyme and Roche. The remaining authors report no conflicts of interest. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the full text and PDF versions of this article on the journal's Web site (www.jneuro-ophthalmology.com). Address correspondence to Alex P. Lange, MD, Vista Klinik, Hauptstrasse 55, Binningen 4102, Switzerland; E-mail: [e-mail] Manogaran et al: J Neuro-Ophthalmol 2016; 36: 363-368 N euromyelitis optica spectrum disorder (NMOSD) is a predominantly a humoral-mediated autoimmune disease, which is typically characterized by episodes of optic neuritis (ON) and transverse myelitis (1,2). For many years, NMOSD had been considered under the umbrella term of multiple sclerosis (MS); it was previously termed optico-spinal MS or Asian MS. Both MS and NMOSD may show similar clinical and neuroimaging features but treatment and prognosis differ significantly (3,4). In addition, MS has relative, but not absolute, preservation of axons with more direct damage to myelin compared with NMOSD (5). Misdiagnosis of NMOSD may occur and lack of appropriate treatment can result in worsening of symptoms and progression. Optical coherence tomography (OCT) is a noninvasive method for measuring retinal nerve fiber layer (RNFL) tissue and macular volume (MV). It has been used in quantifying RNFL in MS and NMOSD patients (5-7). Although there are many cross-sectional studies showing strong correlations between RNFL thickness, total MV, and visual function, we are not aware of any studies of RNFL thinning or MV over time in individuals with NMOSD (8,9). Evaluating these OCT outcome measures over time may be important for defining the window of opportunity within which disease modifying treatment may be administered in clinical trials (10,11). The goal of this longitudinal study was to measure RNFL thickness and MV in NMOSD eyes to determine if, over time, ongoing damage occurs. METHODS Participants Participants were recruited between December 2009 to July 2010 for the first visit and between April 2013 to September 2014 for the second visit with median time between the visits being 46 months (range: 35-55 months). Eligible NMOSD patients were identified from the British Columbia MS database and invited to participate by letter. 363 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution All subjects were diagnosed by an experienced MS neurologist with special interest in NMOSD. Any patient who met the criteria for an NMOSD was included (12). Exclusion criteria included patients with a recent history of ON (,6 months before first visit), patients with clinical ON episodes during follow-up period, patients who did have other clinical symptoms of NMOSD (e.g., transverse myelitis) during follow-up period, history of ocular disease (including macular degeneration, diabetic retinopathy, uveitis, and glaucoma), history of diseases that could mimic NMOSD, neurodegenerative conditions that could impact OCT testing (Parkinson disease, Alzheimer disease), and subjects with difficulty maintaining fixation and/or myopic refraction of more than 25.0 diopters. Low-contrast visual acuity, disease duration, expanded disability status scale (EDSS) scores, treatment history, antibody status, and ON history were also obtained for individuals with NMOSD. All subjects were tested annually for NMOSD antibody status. If the EDSS score was not recent (within 6 months) or if new symptoms were reported, an EDSS examination was performed by an MS neurologist at the time of the OCT testing. The University of British Columbia Clinical Research Ethics Board approved all study procedures. Optical Coherence Tomography Protocol and Analysis The OCT assessment was conducted on the Heidelberg Spectralis spectral domain optical coherence tomography (SD-OCT) device (Software version 5.6.4; Heidelberg Engineering, Heidelberg, Germany) for all participants. An online tracking system was used to compensate for eye movements. Follow-up scans were registered and locked to the initial visit reference image using a tracking software. It was used to identify previous scan locations and "guide" the OCT laser beam to scan the same location again to guarantee maximum reproducibility (13). Retinal Nerve Fiber Layer Thickness Protocol The RNFL protocol was performed in high-resolution mode (axial resolution 3.8 mm, 19,000 scans per second) (7). Sixteen consecutive circular B-scans (each composed of 1,536 A-scans) with a diameter of 3.4 mm were automatically averaged to reduce speckle noise. Several scans were taken by experienced operators and the best centered scans with a quality of at least 25 were chosen for analysis. The software algorithm calculated the objective refraction (spherical equivalent) and the RNFL thickness for the temporal, superior, nasal, and inferior quadrants and the overall mean of these quadrants (global RNFL thickness) were obtained. The RNFL thickness provides a measure of unmyelinated axons that form the optic nerve (7,14). Macular Volume Protocol The MV protocol involved 61 consecutive B-scans (ART 9; 768 A-scans each) horizontally crossing the macula. The 364 software algorithm calculated the total MV and macular thickness automatically. MV provides a measure of both axonal and ganglion cell bodies. Statistical Analysis The scans were analyzed for their reproducibility and mean values were calculated for each time point. Mean global RNFL thickness measurements and mean measurements for each quadrant (superior, temporal, inferior, and nasal), total MV, and macular thickness were extracted and imported into an Excel database. Statistics analysis was performed using the R: a language and environment for statistical computing (R Core Team, 2013). A Shapiro-Wilk normality test determined that the data were normally distributed for all measures. Paired 2-tailed t test was used to compare the OCT measurements over the 2 time points for eyes affected by ON, eyes unaffected by ON, and also for all eyes pooled together. Change in the OCT measures over the 2 time points were also assessed using a 1-sample t test for affected eyes, unaffected eyes, and all eyes together. For affected eyes, unaffected eyes, and all eyes pooled together, 7 pairwise comparisons were conducted and the P-values were adjusted for multiple comparisons using a Hommel correction. Corrected P-values below 0.05 were taken to be significant. RESULTS Twenty five patients were recruited for the first visit and 9 returned for a second visit. The analysis included a total of 9 definite NMOSD participants (Table 1). Six of 9 patients were NMOSD-IgG antibody positive. In 1 subject with difficult fixation, OCT measures could only be obtained for 1 eye. Six of the 9 subjects had bilateral ON history, whereas 2 had ON history only in the right eye and 1 only in the left eye. The temporal, inferior, nasal, or superior quadrant and the mean global RNFL thickness of each NMOSD patient were unchanged compared with baseline for ON affected eyes, unaffected eyes, and all eyes together (Fig. 1 and see Supplemental Digital Content, Table E1, http://links.lww. com/WNO/A203). Similarly, there was no change between the 2 time points for the macular thickness and MV for ON affected eyes, unaffected eyes, and all eyes together (Fig. 2 and see Supplemental Digital Content, Table E1, http:// links.lww.com/WNO/A203). The change in the temporal quadrant RNFL thickness was significant in NMOSD patients for all eyes pooled together (mean = 2.88 mm, SD = 3.7, P = 0.021, Fig. 3C). However, the change in the other OCT measures over time was not significant (Figs. 2B, D, 3, see Supplemental Digital Content, Table E2, http://links. lww.com/WNO/A204). DISCUSSION To the best of our knowledge, this is the first exploratory longitudinal OCT study of patients with NMOSD. Manogaran et al: J Neuro-Ophthalmol 2016; 36: 363-368 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Manogaran et al: J Neuro-Ophthalmol 2016; 36: 363-368 ON History Baseline Patient Sex # of ON Eyes Last ON Disease Antibody OD OS Affected Attack Onset + 1 2 3 4 5 6 7 8 9 2003 2009 2000 1998 2008 2004 1997 1999 2005 Total F F F M F F F F F 8F, 1M Yes Yes No No Yes Yes Yes No Yes 6 yes, 3 no 1 1 1 2 1 1 1 1 0 3 1 3 2 1 1 0 0 1 Bilateral Bilateral Bilateral Bilateral† Bilateral Bilateral OD OD OS 15:3 2010 2010 2010 2004 2008 2006 2009 1999 2006 Follow-Up VA (logMAR) Treatment EDSS Age (yr) OD Mitoxantrone Azathioprine Mitoxantrone Azathioprine None CellCept None Rituximab Mitoxantrone 4.0 1.5 4.0 3.5 2.0 3.5 NA 2.0 6.0 47 40 18 37 41 57 61 59 52 0.21 0 0.21 NA 0.3 0.21 0.6 0.21 0 OS VA (logMAR) Treatment 1.3 Rituximab 0.4 Rituximab 1.3 Rituximab 0.1 Azathioprine 0.4 None 0.21 CellCept 0 None 0.1 Rituximab 0 Rituximab 3.5‡ 46§ (14) 0.22§ 0.42§ (1.5-6.0) (0.19) (0.52) EDSS Age (yr) OD OS 3.5 2.0 3.0 4.0 2.0 4.0 4.0 2.0 5.5 50 44 21 41 46 60 64 62 55 0.21 0 0.5 NA 0.21 0.21 0.4 0.21 20.1 1.3 0 0.21* 0.21 0.3 20.1 0.1 0 20.1 3.5‡ 49§ 0.21§ 0.21§ (2.0-5.5) (13) (0.19) (0.43) Original Contribution Row labeled total mean with SD in parenthesis, except for EDSS, which has the median and range in parenthesis. *Subject had cataract surgery between baseline and follow-up examination. † Had only 1 bilateral ON episode. ‡ Median score (range). § Mean (SD). # of ON, number of ON attacks; Antibody +, if subject was NMOSD antibody positive; EDSS, expanded disability status scale; NMOSD, neuromyelitis optica spectrum disorder; ON, optic neuritis; OD, right eye; OS, left eye; VA, visual acuity. 365 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. TABLE 1. Characteristics of NMOSD patients at baseline and follow-up visit Original Contribution FIG. 1. RNFL thickness in NMOSD patients for each quadrant and the average RNFL thickness in (A) ON affected eyes, (B) ON unaffected eyes, and (C) all eyes pooled together. Inf, inferior; Nas, nasal; NMOSD, neuromyelitis optica spectrum disorder; ON, optic neuritis; RNFL, retinal nerve fiber layer; Sup, superior; Temp, temporal. Previously, only cross-sectional studies had been performed (5,6,15). In our report, no significant changes were detected in RNFL thickness, macular thickness, or volume in the NMOSD group over a period of 4 years. However, there was a statistically significant change in RNFL thickness in the temporal quadrant of NMOSD subjects. This is in contrast to findings in patients with MS. Talman et al (11) conducted a longitudinal study of FIG. 2. Macular measurements performed in NMOSD patients. A and B, macular volume; C and D, macular thickness. NMOSD, neuromyelitis optica spectrum disorder. 366 Manogaran et al: J Neuro-Ophthalmol 2016; 36: 363-368 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution FIG. 3. The change in RNFL thickness for each quadrant and average RNFL thickness between the 2 time points in NMOSD subjects for (A) ON affected eye, (B) ON unaffected eyes, and (C) all eyes pooled together. NMOSD, neuromyelitis optica spectrum disorder; ON, optic neuritis; RNFL, retinal nerve fiber layer. 593 MS eyes using a time domain-OCT system for more than 3 years. An average of 2 mm decrease in RNFL thickness was found for each year of follow-up in MS patients and for healthy controls, there was only a 0.49 mm decrease in RNFL thickness. In contrast, a recent longitudinal study using SD-OCT found no change in RNFL thickness over time in 37 relapsing remitting multiple sclerosis and 10 secondary progressive multiple sclerosis patients (13). The authors of this study noted that the changes observed in previous studies may have been due to an older model of the OCT system and that the intersubject variability in RNFL thickness is high. Yet, in the report in which SD-OCT was used, 24 months is insufficient follow-up to detect a decrease of 2 mm per year because the axial resolution of the machine is 3.8 mm. Previous cross-sectional studies of MS patients (14,16) also documented RNFL thinning and a negative correlation with disease duration even in the absence of ON, suggesting ongoing axonal loss over time. Similar studies in NMOSD patients did not show similar results (7). The reason was thought to be due to difference in pathophysiology to the 2 diseases. Histopathologically, NMOSD is characterized by acute inflammation associated with neutrophilic and eosinophilic infiltrate, demyelination, and destructive necrotizing cavitation, with vascular hyalinization and IgG and complement deposition, which destroys perivascular neural parenchyma (6,17). The intense inflammatory activity in NMOSD eyes can result in pronounced RNFL atrophy. However, MS lesions exhibit demyelination and inflammaManogaran et al: J Neuro-Ophthalmol 2016; 36: 363-368 tion with less axonal loss than in NMOSD (18). In addition, subclinical inflammation in MS leads to ongoing brain and RNFL atrophy, whereas in NMOSD patients, only acute attacks are expected to affect RNFL thickness (6). Our results of stable RNFL thickness in patients with NMOSD over 4 years would support this theory. We did find a significant change in RNFL thickness in the temporal quadrant over 4 years in NMOSD subjects. Previous studies have documented a similar decrease in RNFL thickness of the temporal quadrant in MS patients over time (11,15,19,20). The decreased thickness might be due to subclinical disease activity, well recognized in MS but only recently appreciated in NMOSD (21,22). Possibly, subclinical disease activity in NMOSD may be occurring at a slower rate than in MS, and the temporal quadrant is most sensitive to this change because of the large number of ganglion cell axons in the papillomacular bundle (23). Further investigations using segmented retinal layer analysis might provide more insight on this OCT finding. There are some limitations to our study. The sample size of patients was small. The lack of change over time may be due to the small patient cohort. The effect of treatment on the visual pathway is currently unknown. Data were only collected at 2 different time points over the 4 years and future studies should look at NMOSD subjects at multiple time points over a longer period. Finally, a control group was not used in this study, so any comments made on 367 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution differences between MS, NMOSD, and healthy controls is only speculative. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: P. Manogaran, A. L. Traboulsee, and A. P. Lange; b. Acquisition of data: P. Manogaran, A. L. Traboulsee, and A. P. Lange; c. Analysis and interpretation of data: P. Manogaran, A. L. Traboulsee, and A. P. Lange. Category 2: a. Drafting the article: P. Manogaran, A. L. Traboulsee, and A. P. Lange; b. Revising it for intellectual content: P. Manogaran, A. L. Traboulsee, and A. P. Lange. Category 3: a. Final approval of the completed article: P. Manogaran, A. L. Traboulsee, and A. P. 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