Neuromyelitis optica spectrum disorder (NMOSD) is classified as an astrocytopathy often characterized by devastating neurological sequelae (1,2). Although this disorder classically affects optic nerve and spinal cord, a report of the International Consensus Diagnostic Criteria for NMOSD (IPND 2015) included a range of clinical phenotypes (3). Although detection of aquaporin-4 antibodies (AQP4-Ab) is not an absolute requirement for the diagnosis of NMOSD, they are rarely found in healthy individuals or patients with other inflammatory central nervous system (CNS) disorders (4–6). Although monophasic or recurrent optic neuritis (ON) is a core clinical characteristic of NMOSD, at disease onset the clinician is confronted with a broad range of etiologies. Establishing the correct diagnosis is essential to implement appropriate treatment to give the patient the best possible visual outcome.
The aim of our study was to report in a cohort of Argentinian patients with ON, the clinical features at onset, and final vision at 6 months of those who were positive for AQP4-Ab (P-ON) vs those who were negative for AQP4-Ab (N-ON) or having other causes of ON.
Patients from Buenos Aires, Argentina, diagnosed with a first episode on ON (clinically isolated acute ON) were enrolled. A total of 57 consecutive patients who visited the Department of Neurology and Neuro-opthalmology for possible CNS inflammatory disease, without evidence of a metabolic, toxic, infectious, hereditary, vascular, or compressive etiology, between 2009 and 2015 were tested for AQP4-Ab. Ultimate diagnostic categories included AQP4-Ab–positive NMOSD-ON (P-NMOSD-ON), AQP4-Ab–negative NMOSD-ON (N-NMOSD-ON), multiple sclerosis ON (MSON), chronic relapsing inflammatory ON (CRION), single isolated ON (SION), and other causes (7). AQP4-Ab–positive or AQP4-Ab–negative NMOSD was defined according to the International Consensus Diagnostic Criteria (3). ON was defined as visual loss and at least 2 of the following criteria: relative afferent pupillary defect, color desaturation, pain on eye movement, abnormal visual evoked response, and visual field defect (8,9). All patients were evaluated by at least one neurologist and/or one ophthalmologist during and after the first attack. Visual acuity impairment was assessed at baseline and after 6 months in each eye by an ordinal scale according to Wingerchuck et al (10): 0 = normal; 1 = scotoma but visual acuity better than 20/30; 2 = visual acuity of 20/30–20/59; 3 = visual acuity of 20/60–20/199; 4 = visual acuity of 20/200–20/800; 5 = counting fingers only; 6 = light perception; and 7 = no light perception and its equivalent on logarithm of the minimum angle of resolution (LogMAR). The final visual outcomes for bilateral ON (BON) were based on the eye with worse visual acuity at 6 months. Visual impairment was defined as mild (scale: 0–2 or ≤0.4 LogMAR), moderate-severe (scale: 3–4 or from 0.5 to 1.9 LogMAR), and very severe (scale: 5–7 or ≥2 LogMAR). Patients with light perception or no light perception (6–7 on Wingerchuck scale) were excluded from the LogMAR analysis. Patient evaluation included brain (coronal, axial, and sagittal) and spinal cord (axial and sagittal) magnetic resonance imaging (MRI) performed on a 1.5-T scanner. Cerebrospinal fluid analysis included testing for oligoclonal bands (evaluated by isoelectric focusing), whereas a tissue-based indirect immunofluorescence (IIF) technique was used to detect AQP4-Ab (1,11). Positive antinuclear antibodies (ANAs, IIF using Hep-2 Cell culture) were defined as ≥1:160. Other diagnostic tests were performed according to clinical suspicion for a specific diagnosis. All patients were treated with intravenous methylprednisolone (1 g/d) for 3 days during the initial episode of ON.
Statistical analysis was performed using Statistical Program for Social Sciences (SPSS) (version 22.0) and Graph-Pad Prism 6 software. We performed 2 sample t tests or the Mann–Whitney U-tests for continuous data and Fisher exact test or χ2 test for categorical data for the comparisons of P-ON vs N-ON patients, when appropriate. For ordinal regression (cumulative logit model), the whole cohort was evaluated according to Wingerchuck score where 7 is the lowest visual acuity level and 0 represents the highest visual acuity level. At 6 months, we applied a multivariate analysis to assess the impact of different factors (AQP4-Ab status, age at onset, recurrence of ON, unilateral or BON at onset, Winguerchuck score at recovery from first ON attack, and immunosuppressive therapy) on final visual outcomes. The Kruskal–Wallis test (nonparametric test) was used to estimate differences between more than 2 groups (etiological subgroups), and the post hoc analysis was performed using Dunn multiple comparison tests, when appropriate. For all the analyses, the significance level was established as P < 0.05.
A total of 57 patients were included. The demographic, clinical, serologic, and MRI features of P-ON vs N-ON patients are summarized in Table 1. The frequency of AQP4-Ab positivity in our patient cohort was 29.82%, P-ON was only found in patients with NMOSD. N-ON group included MSON (n = 14, 24.56%), N-NMOSD-ON (n = 5, 8.77%), CRION (n = 5, 8.77%), SION (n = 8, 14.03%), and others (antiphospholipid syndrome ON [n = 3, 5.26%], Sjögren syndrome ON [n = 2, 3.50%], neurosarcoidosis ON [n = 2, 3.50%], and rheumatoid arthritis ON [n = 1, 1.75%]) (Table 2). At follow-up, we did not find any significant difference between P-ON vs N-ON patients regarding ON relapses, frequency of oligoclonal bands, ANA, and brain MRI lesions. However, longitudinally extensive transverse myelitis (lesions ≥3 spinal segment) on spinal cord MRI was associated with P-ON (P = 0.04), and normal spinal cord MRI was associated with N-ON (P = 0.03). Although not statistically significant, compared to P-ON patients, we observed that N-ON group had visual acuity 20/40 or better (27.5% vs 11.7%, P = 0.30), and was associated with recovery to visual acuity 20/40 or better at 6 months (65% vs 58.8%, P = 0.76). In addition, more often P-ON patients had a visual acuity worse than or equal to 20/200 at baseline (76.4% vs 65%, P = 0.12) and after 6 months (29.5% vs 27.5%, P = 0.88). Forty-one percent of the P-ON group and 27.5% of the N-ON group were excluded from the initial logMAR analysis because they had light perception or no light perception at baseline, and 5.8% in the P-ON group and 12.5% in the N-ON group also were excluded from final logMAR visual acuity for the same reason. The P-ON group had more severe visual loss with initial ON (logMAR VA in P-ON: 1.15 vs VA in N-ON: 0.95, P = 0.48) and a worse final visual acuity (final visual acuity in P-ON: 0.51 vs final logMAR visual acuity in N-ON: 0.38, P = 0.43). However, none of these trends were statistically significant. Poor visual acuity after the first attack was associated with worse visual acuity at 6 months (odds ratio = 2.28, 95% CI [2.90–15.52], P = 0.03) after applying the ordinal regression model (R2 Nagelkerke = 0.446).
In this consecutive cohort of patients with inflammatory ON, seroprevalence of AQP4-Ab was relatively high (29.82%) compared with American and European populations (12,13), but lower compared with Asian population (14). These variations may be due to multiple factors. Ethnic heterogeneity between Asian, Latin American, European, and American populations is likely one factor. In the Asian population, the frequency of HLA-DPB1* 0501 is higher (44.9%–73.1%) than in whites (2.6%–5.3%) and in association with AQP4-Ab seropositivity in Han Chinese (15). P-ON was found in 77% of patients with NMOSD, consistent with previously published data where AQP4-Ab detected by IIF was found in 54%–73% of patients with NMOSD (2). Methodology used for detection of AQP4-Ab also is a factor that explains the differences among populations. In our cohort, we acknowledge that only IIF was used for assessment of AQP4-Ab serostatus. This was a limitation of our study given that other reports have shown that a cell-based assay is a more sensitive method (12–16).
We did not find statistically significant differences between P-ON vs N-ON patients with regard to visual acuity at baseline and after 6 months, ON recurrence, oligoclonal band frequency, ANA, and brain MRI lesions. Previous studies have found that P-ON patients are more frequently young, females and have more severe visual acuity loss (7,12,13,16). By contrast, we found a statistically significant association in the P-ON group regarding male sex (P = 0.02) and earlier age of onset (P = 0.01) compared with N-ON patients. Also, P-ON patients had poor visual acuity at onset (4.85 ± 1.74) consistent with previously published data (17).
We found that BON was more frequently observed in the P-ON group compared with the N-ON group. This feature resembles the European more than Asian population (17,18). There was a trend toward use of immunosuppressant therapy at the first clinical event of ON in the P-ON group.
We are aware of limitations to our study. It was retrospective in design with a limited number of patients, short follow-up period, and possible selection bias. We used IIF to assess AQP4-Ab, and possibly, more patients would have been seropositive using more sensitive methods. Also, myelin oligodendrocyte glycoprotein antibodies are not available at our centers, and this likely affected our diagnostic categories. Both SION and CRION groups might have developed NMOSD, MS, or other systemic disorders if they had a longer follow-up period.
In conclusion, our study adds to the international data set of evaluating P-ON patients. Further prospective and multicenter studies from South America with larger numbers of patients will help expand our initial findings, hopefully leading to more specific diagnostic categories and improved treatment options for patients with ON.
We thank Dr. Florencia Ocariz and Adrian Rubstein for their critical reading of the manuscript and valuable recommendations.
STATEMENT OF AUTHORSHIP
Category 1: a. Conception and design: E. Carnero Contentti; b. Acquisition of data: E. Carnero Contentti, J. Celso, and M. De Virgiliis; c. Analysis and interpretation of data: E. Carnero Contentti and M. De Virgiliis. Category 2: a. Drafting the manuscript: E. Carnero Contentti, S. Morales, M. De Virgiliis, and A. Gomez; b. Revising it for intellectual content: E. Carnero Contentti, M. De Virgiliis, J. P. Hryb, A. Gomez, S. Morales, J. Celso, F. Leguizamón, E. Chiganer, J. L. Di Pace, C. Lessa, and M. Perassolo. Category 3: a. Final approval of the completed manuscript: E. Carnero Contentti, M. De Virgiliis, J. P. Hryb, A. Gomez, S. Morales, J. Celso, F. Leguizamón, E. Chiganer, J. L. Di Pace, C. Lessa, and M. Perassolo.
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