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Background and purpose: Cerebrospinal fluid (CSF) kappa free light chains (FLCs) may be a more sensitive marker of intrathecal immunoglobulin (Ig)G synthesis compared with oligoclonal bands (OCBs). Our aim was to retrospectively determine the additional value of the kappa and lambda index (CSF FLC/serum FLC)/(CSF albumin/serum albumin) in predicting a multiple sclerosis (MS) diagnosis in a group of OCB‐negative patients with suspected MS. Methods: The CSF and serum kappa and lambda FLCs were tested using the Freelite kit (serum) and Freelite Mx (CSF) assay (The Binding Site Group, Bimingham, UK) in 391 OCB‐negative patients with suspected/possible MS and in 54 OCB‐positive patients with MS. Results: The CSF kappa FLC levels were below the detection limit (0.27 mg/L) in 61% of patients. Using quantitative data, we found the best kappa index cut‐off value for the prediction of MS to be 5.8. A kappa index ≥5.8 was present in 25% of OCB‐negative MS (23/92) and in 98% of OCB‐positive patients with MS. Using a qualitative approach and a kappa index cut‐off of 5.9, based on literature data, we likewise found that 24% of OCB‐negative patients with MS had a kappa index ≥5.9, compared with 5.4% of OCB‐negative patients without MS (P < 0.001). No reliable data could be obtained for the lambda index; lambda FLCs were below the detection limit (0.68 mg/L) in 90% of CSF samples. Conclusions: The kappa index could contribute to the identification of OCB‐negative patients with a high probability of an MS diagnosis. Using more sensitive techniques might even improve the diagnostic performance of the kappa index and better define the role of the lambda index. [ABSTRACT FROM AUTHOR]

Objective: To describe onset clinical features predicting time to first relapse and time to long-term visual, motor and cognitive disabilities in paediatric-onset aquaporin-4 antibody (AQP4-IgG) neuromyelitis optica spectrum disorders (NMOSDs)., Methods: In this retrospective UK multicentre cohort study, we recorded clinical data of paediatric-onset AQP4-IgG NMOSD. Univariate and exploratory multivariable Cox proportional hazard models were used to identify long-term predictors of permanent visual disability, Expanded Disability Status Scale (EDSS) score of 4 and cognitive impairment., Results: We included 49 paediatric-onset AQP4-IgG patients (38.8% white, 34.7% black, 20.4% Asians and 6.1% mixed), mean onset age of 12±4.1 years, and 87.7% were female. Multifocal onset presentation occurred in 26.5% of patients, and optic nerve (47%), area postrema/brainstem (48.9%) and encephalon (28.6%) were the most involved areas. Overall, 52.3% of children had their first relapse within 1 year from disease onset. Children with onset age <12 years were more likely to have an earlier first relapse (p=0.030), despite showing no difference in time to immunosuppression compared with those aged 12-18 years at onset. At the cohort median disease duration of 79 months, 34.3% had developed permanent visual disability, 20.7% EDSS score 4 and 25.8% cognitive impairment. Visual disability was associated with white race (p=0.032) and optic neuritis presentations (p=0.002). Cognitive impairment was predicted by cerebral syndrome presentations (p=0.048), particularly if resistant to steroids (p=0.034)., Conclusions: Age at onset, race, onset symptoms and resistance to acute therapy at onset attack predict first relapse and long-term disabilities. The recognition of these predictors may help to power future paediatric clinical trials and to direct early therapeutic decisions in AQP4-IgG NMOSD., Competing Interests: Competing interests: VC reports funding from the European Charcot Foundation supporting for the present manuscript. No award/grant number. SM reports grants from Biogen, Novartis, Bayer, Merck, Almirall and Roche; RD reports grants from Barts Charity, MS Society of Great Britain, Horne Family Charitable Trust and Celgene; grants and consulting fees from Merck and Biogen, consulting fees from Roche, Teva, Sanofi Genzyne and Janssen; MJL reports consulting fees from Advisory Board Octapharma and from Advisory Board Novartis; non-financial support from Advisory Board CSL Behring; grants from NIHR, GOSH Charity and Action Medical Research; CH reports consulting fees from Novartis, Biogen, UCB and Roche; JP reports grants and consulting fees from Merck Serono, Novartis, Biogen Idec, Teva, Abide and Bayer Schering; grants from MS Society and Guthie Jackson Foundation; payment for expert testimony and support for attending meetings and/or travel from Chugai Pharma and Bayer Schering, Alexion, Genzyme, MedImmune, EuroImmun, MedDay and ARGENX., (© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.)