Common comorbidities and survival in MS: Risk for stroke, type 1 diabetes and infections

Background: Survival in MS has increased during the era of disease modifying therapies, but life expectancy in MS patients is still reduced by several years. Increased risk for common comorbidities related to brain health, such as risk for circulatory diseases have been reported in MS and could affect survival. In this paper, we studied age- and gender adjusted risks for circulatory diseases and related disorders, and their impact on overall MS survival in population of Southwest Finland.

Materials and methods: The ICD-10 codes for hospital visits were searched from the administrative data pool from 1.1.2004 up to 31.12.2012 for the resident MS and control cases at the Hospital District of Southwest Finland. The MS population under study consisted of prevalent cases in 1.1.2004 and new cases from 1.1.2004 followed up to death or 31.12.2012. Patient documents were scrutinized to confirm the MS diagnosis (G 35) by the McDonald´s criteria and to confirm the diagnoses and causes of death for the cerebro- and cardiovascular diagnoses under study. The randomly chosen 10-fold control population was matched by birth year and gender to calculate the coincident risks (odds ratio, OR) with 95% confidence intervals (95% CI) and another separate control population from the same patient pool was used to verify the stability of the results. P-values were calculated using Pearson's χ2 test. The Kaplan- Meier analysis log rank test was applied to study survival.

Results: During the follow-up 1074 confirmed MS cases were treated in the hospital district, including the deceased cases after 1.1.2004 (5.9%). The probability of survival was 82.4 years among MS and 85.6 years among the control cases, log rank p < 0.001. The survival disadvantage within MS was associated with comorbidity for circulatory disease codes in ICD -10: I06-I71, log rank p < 0.001. The specific risk for ischemic and haemorrhagic stroke was significant with high OR of 1.49 (95% CI 1.03- 2.35) and 2.5 (1.24-5.06) respectively. The two-fold risk for type 1 diabetes in MS was significant, OR 2.1 (1.3-3.36). The main causes of death among the MS cases were infections and the coincident high risk for several infections was significant. There was no difference in the risk for acute myocardial infarct, transient ischemic attack, atrial fibrillation, hypertension, or obesity in comparison with the control cases.

Conclusions: Given the high risk for stroke in this MS population and the observed complexity among the coincident common risk factors for circulatory diseases, the high risk for type 1 diabetes and common infections raise a need to recognize patients at risk with these conditions and with the other known risk factors such as metabolic syndrome and smoking. The survival disadvantage related to circulatory diseases observed in general population is true also in MS and should be recognized to reduce the burden of disease and premature mortality in MS.