Page 87 - The autoimmune hypothesis of narcolepsy and its unexplored clinical features M.S. Schinkelshoek

Statistical analysis
Differences at baseline in participant characteristics between the SXB and modafinil group were calculated with Mann-Whitney U (age), chi-square (gender, co-medication), and Student’s t-tests (baseline BMI, treatment duration). To estimate if the BMI of the study cohort was significantly higher than that of the general Dutch population, data from Statistics Netherlands (Centraal Bureau voor de Statistiek, 2016) were used.
To assess whether statistically significant BMI changes occurred during follow-up, a paired sample Student´s test was performed to compare BMI at baseline with BMI at the last visit for four separate groups (based on gender and treatment). Since this comparison is still subject to factors influencing BMI and there was a single outcome parameter, a linear mixed model with a random slope and a random intercept for each individual was fitted. The outcome was the difference in BMI with respect to baseline. As fixed effects we added medication, gender, baseline BMI and follow-up duration, and also the interactions of medication, gender and baseline BMI with follow-up duration. Normality of the fitted mixed model was subsequently assessed using scatter plots and quantile-quantile plots of the model’s residuals. Correlations between medication dose and BMI change for individual patients were assessed using Spearman’s rank-order correlation tests. P-values below 0.05 were deemed significant. Bonferroni corrections were executed when needed. All analyses were conducted using the IBM SPSS Statistics 23 software package.
Results
Patient characteristics
59 individuals started treatment with SXB and 22 with modafinil (Table 5.1). Follow-up frequency and duration varied considerably among patients (range 0.14-6.94 years). There were no significant differences found in age and baseline BMI between groups. More males were in the SXB group. Mean duration of treatment for the SXB group was longer than that of the modafinil group.
Medication and BMI change
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