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Objectives: To estimate the nationwide population-based incidence, prevalence, and geographical distribution of neuromyelitis optica (NMO) spectrum disorder (NMOSD) in Denmark based on the 2015 International Panel for NMO Diagnosis (IPND) criteria., Methods: We conducted a multicentre, historically prospective study. Data were sourced from the Danish National Patient Registry, the Danish Multiple Sclerosis Registry, departments of neurology, and laboratories providing aquaporin-4 antibody test. Cases were selected based on the 2006 Wingerchuk and the 2015 IPND criteria and were individually validated by an expert panel., Results: We confirmed NMO in 30 cases (2006 criteria) and NMOSD in 56 cases (2015 IPND criteria) between 2007 and 2014. Defined by the 2006 criteria, the incidence of NMO was 0.029 per 100,000 person-years (95% confidence interval [CI] 0.014-0.051), and the prevalence (aged 16 years and older) was 0.566 per 100,000 (95% CI 0.370-0.830). Based on the 2015 IPND criteria, the incidence of NMOSD was 0.070 per 100,000 person-years (95% CI 0.046-0.102), and the prevalence (aged 16 years and older) was 1.09 per 100,000 (95% CI 0.808-1.440), without regional differences., Conclusions: Our estimates of incidence and prevalence are similar to other Caucasian population-based studies using the 2015 IPND criteria. We found no geographical clustering in Denmark., (Copyright © 2018 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)

Objective: To describe the pattern of development of incidence of multiple sclerosis (MS) over 60 years in Denmark with age-period-cohort analyses and seasonality of birth., Methods: Data on virtually all patients with onset of MS have since 1950 been prospectively recorded and kept in the Danish Multiple Sclerosis Registry with multiple sources of notification. Annualized incidence rates per 100,000 were directly standardized to the European Standard Population., Results: We have registered 19,536 cases with clinical onset of confirmed MS in Denmark from 1950 to 2009. From the 1950-1959 to the 2000-2009 onset period, incidence more than doubled in women, with an increase from 5.91 (95% confidence interval [CI]: 5.60-6.24) to 12.33 (95% CI: 11.91-12.75) per 100,000 per year compared with a modest 24% increase in men from 4.52 (95% CI: 4.24-4.81) to 6.08 (95% CI: 5.79-6.38). With age at onset of 50 years and older, incidence increased with a factor 4.30 in women and 2.72 in men. The female/male sex ratio increased over time and with year of birth. Age-period-cohort analysis revealed a significant birth cohort effect in addition to the age and period effect. We found no statistically significant seasonality of births., Conclusion: The incidence of MS has doubled in women, most pronounced with late onset, and has only modestly increased in men. Lifestyle changes in the female population that could include fewer childbirths, increased occurrence of obesity, and increased cigarette consumption may have a role., (© 2018 American Academy of Neurology.)

Objective: To investigate whether smoking in patients with relapsing-remitting multiple sclerosis (RRMS) treated with interferon beta (IFN-β) is associated with the relapse rate and whether there is an interaction between smoking and human leukocyte antigen (HLA)-DRB1*15:01, HLA-A*02:01, and the N-acetyltransferase-1 ( NAT1 ) variant rs7388368A., Methods: DNA from 834 IFN-β-treated patients with RRMS from the Danish Multiple Sclerosis Biobank was extracted for genotyping. Information about relapses from 2 years before the start of treatment to either the end of treatment or the last follow-up visit was obtained from the Danish Multiple Sclerosis Treatment Register. Smoking information came from a comprehensive questionnaire., Results: We found that the relapse rate in patients with RRMS during IFN-β treatment was higher in smokers compared to nonsmokers, with an incidence rate ratio (IRR) of 1.20 (95% confidence interval [CI] 1.021-1.416, p = 0.027) and with an IRR increase of 27% per pack of cigarettes per day (IRR 1.27, 95% CI 1.056-1.537, p = 0.012). We found no association or interaction with HLA and the NAT1 variant., Conclusion: In this observational cohort study, we found that smoking is associated with increased relapse activity in patients with RRMS treated with IFN-β, but we found no association or interaction with HLA or the NAT1 variant., (© 2018 American Academy of Neurology.)

Objective: To investigate the effect of chronic comorbidity on the time of diagnosis of multiple sclerosis (MS) and on mortality in MS., Methods: We conducted a population-based, nationwide cohort study including all incident MS cases in Denmark with first MS symptom between 1980 and 2005. To investigate the time of diagnosis, we compared individuals with and without chronic comorbidity using multinomial logistic regression. To investigate mortality, we used Cox regression with time-dependent covariates, following study participants from clinical MS onset until endpoint (death) or to the end of the study, censuring at emigration., Results: We identified 8,947 individuals with clinical onset of MS between 1980 and 2005. In the study of time of diagnosis, we found statistically significant odds ratios for longer diagnostic delays with cerebrovascular comorbidity (2.01 [1.44-2.80]; <0.0005), cardiovascular comorbidity (4.04 [2.78-5.87]; <0.0005), lung comorbidity (1.93 [1.42-2.62]; <0.0005), diabetes comorbidity (1.78 [1.04-3.06]; 0.035), and cancer comorbidity (2.10 [1.20-3.67]; 0.009). In the mortality study, we found higher hazard ratios with psychiatric comorbidity (2.42 [1.67-3.01]; <0.0005), cerebrovascular comorbidity (2.47 [2.05-2.79]; <0.0005), cardiovascular comorbidity (1.68 [1.39-2.03]; <0.0005), lung comorbidity (1.23 [1.01-1.50]; 0.036), diabetes comorbidity (1.39 [1.05-1.85]; 0.021), cancer comorbidity (3.51 [2.94-4.19]; <0.0005), and Parkinson disease comorbidity (2.85 [1.34-6.06]; 0.007)., Conclusions: An increased awareness of both the necessity of neurologic evaluation of new neurologic symptoms in persons with preexisting chronic disease and of optimum treatment of comorbidity in MS is critical., (© 2017 American Academy of Neurology.)

Objective: As previous research has suggested that exposure to vitamin D insufficiency in utero may have relevance for the risk of multiple sclerosis (MS), we aimed to examine the direct association between level of neonatal vitamin D and risk of MS., Methods: We carried out a matched case-control study. Dried blood spots samples (DBSS) belonging to 521 patients with MS were identified in the Danish Newborn Screening Biobank. For every patient with MS, 1-2 controls with the same sex and birth date were retrieved from the Biobank (n = 972). Level of 25-hydroxyvitamin D (25[OH]D) in the DBSS was measured using liquid chromatography tandem mass spectroscopy. The association between different levels of 25(OH)D and risk of MS was evaluated by odds ratios (OR) calculated in conditional logistic regression models., Results: We observed that lower levels of 25(OH)D in neonates were associated with an increased risk of MS. In the analysis by quintiles, MS risk was highest among individuals in the bottom quintile (<20.7 nmol/L) and lowest among those in the top quintile of 25(OH)D (≥48.9 nmol/L), with an OR for top vs bottom of 0.53 (95% confidence interval [CI] 0.36-0.78). In the analysis treating 25(OH)D as a continuous variable, a 25 nmol/L increase in neonatal 25(OH)D resulted in a 30% reduced risk of MS (OR 0.70, 95% CI 0.57-0.84)., Conclusion: Low concentrations of neonatal vitamin D are associated with an increased risk of MS. In light of the high prevalence of vitamin D insufficiency among pregnant women, our observation may have importance for public health., (© 2016 American Academy of Neurology.)

We estimated survival probability and excess death rates for patients with MS on the basis of data from the Danish Multiple Sclerosis Registry, which includes virtually all patients diagnosed with MS in Denmark (population, five million) since 1948. We reviewed and reclassified all case records according to standardized diagnostic criteria. By linkage to the Danish Central Population Registry, we lost to follow-up only 25 patients who had emigrated. The median survival time from onset of the disease was 28 years in men (compared with 40 years in the matched general male population) and 33 years in women (versus 46 years). The median survival time from diagnosis was 22 years in men (versus 37 years) and 28 years in women (versus 42 years). The excess death rate between onset and follow-up (observed deaths per 1,000 person-years minus the expected number of deaths in a matched general population) was 14.3 in men, which was significantly higher than in women (12.0). Excess mortality increased with age at onset of MS in people of each sex. The 10-year excess death rate has decreased significantly in recent decades. Excess mortality was highest in cases with cerebellar symptoms at onset.