To Örebro University

Introduction: Substantial progress in the treatment of multiple sclerosis (MS) has been made since the 1990s. However, the presence of comorbidity and the impact of treatment are less defined. Here we determined rates of comorbidity before and after MS diagnosis as compared with a matched MS-free population.

Methods: A national incident MS cohort diagnosed in 2008-2016 was identified in the Swedish National Patient Register with data further linked to the national Prescribed Drug Register and Cause of Death Register. In addition, a sub-cohort of MS patients was identified in the electronic medical records (EMR) of the Karolinska University Hospital. MS patients were matched with and compared to 10 MS-free individuals by age, sex, and region of residence. Incidence rates (IR) per 10,000 person-years and incidence rate ratios (IRR) of comorbidities were calculated after MS diagnosis.

Results: In total, 6,602 MS patients were identified in the national cohort and were compared with 61,828 MS-free controls (female, 69%; median age, 40 years), while a sub-cohort from one hospital of 1,289 patients had a MS diagnosis recorded in EMR and was compared with 11,721 individuals without MS (female, 68%; median age, 37 years). The national MS cohort had higher proportions before MS diag-nosis compared with MS-free controls of autoimmune disease (1.3% vs 0.7%), bladder dysfunction (1.2% vs 0.2%), retinal disorders (2.4% vs 1.2%) and epilepsy (1.5% vs 0.8%). Similar patterns were observed for the single-hospital cohort, except for epilepsy. Bipolar disorder was more common among single-hospital MS patients (1.6% vs 0.7%).After MS diagnosis, patients in the national cohort had higher IR compared with MS-free controls of autoimmune disease (IRR 3.60; 95% confidence interval [CI], 2.88-4.51), bladder dysfunction (IRR 47.44; 95% CI, 36.81-61.14) and epilepsy (IRR 2.36; 95% CI, 1.75-3.17). Similar patterns were observed in the single-hospital cohort. Toxic liver disease was higher (IRR 3.51; 95% CI 1.37-8.98) in the MS cohort in the national cohort only, while bipolar disorder was higher only in the single-hospital cohort (IRR 1.88; 95% CI 1.10-3.22).

Conclusions: Before a diagnosis of MS, patients already displayed an increased rate of comorbidity compared with MS-free controls. After diagnosis, patients with MS continued to display increased risk of several comorbidities, some of which may be explained by surveillance bias due to more frequent contact with healthcare.