This is an interesting study conducted using the Swedish National Patient Register looking at the risk of developing MS in patients with psychiatric disorders. The paper showed that patients with depression and bipolar disorder are more likely to develop MS but that patients with schizophrenia are less likely to develop MS.
This study has a number of advantages over similar studies conducted in the past. The Swedish national database provides a huge amount of information allowing the investigators to look at what they state is ‘the largest cohort ever employed for such a purpose’. It also used a control population and a matched sibling design to ensure that the trends discovered cannot just be accounted for by genetic inheritance and therefore by coincidence.
One potential weakness of such studies can sometimes be the conundrum of cause and effect, i.e. is the MS causing depression due to the psychological burden of the condition. In this study, the risk of MS was independent of the time of onset of the psychiatric condition i.e. MS may have occurred before or after the onset of bipolar disorder or depression.
The study investigators conclude that this association may be explained by a general inflammatory process in the CNS. They claim it is not likely to be simply due to the psychological burden of MS because there appears to be no temporal relationship between the occurrence of bipolar disorder or depression and the onset of MS. Other possible hypotheses include MS treatments as a possible trigger (steroids/interferon beta) and environmental factors i.e. that those with psychiatric conditions are more likely to smoke and stay indoors thus depriving themselves of vitamin D.
This is a fascinating study which suggests a possible common mechanism between psychiatric conditions and MS. However, I note MSers responses to similar posts of this kind where pseudobulbar affect had been mistaken for bipolar disorder. One possible next step would be to investigate whether drugs targeting MS have any effect on the symptoms of these psychiatric disorders and this would strengthen the hypothesis that the underlying mechanisms are related.
Prof G’s previous post on bipolar disorder and MS
Mult Scler. 2014 Jul 10. pii: 1352458514540970. [Epub ahead of print]
Multiple sclerosis and psychiatric disorders: Comorbidity and sibling risk in a nationwide Swedish cohort.
Background: Psychiatric disorders are known to be prevalent in multiple sclerosis (MS).
Objective: The objective of this paper is to study comorbidity between MS and bipolar disorder, schizophrenia and depression in a nationwide cohort and to determine whether shared genetic liability underlies the putative association.
Methods: We identified ICD-diagnosed patients with MS (n = 16,467), bipolar disorder (n = 30,761), schizophrenia (n = 22,781) and depression (n = 172,479) in the Swedish National Patient Register and identified their siblings in the Multi-Generation Register. The risk of MS was compared in psychiatric patients and in matched unexposed individuals. Shared familial risk between MS and psychiatric disorders was estimated by sibling comparison.
Results: The risk of MS was increased in patients with bipolar disorder (hazard ratio (HR) 1.8, 95% confidence interval (CI) 1.6–2.2, p < 0.0001) and depression (HR 1.9, 95% CI 1.7–2.0, p < 0.0001). MS risk in schizophrenia was decreased (HR 0.6, 95% CI 0.4–0.9, p = 0.005). The association between having a sibling with a psychiatric disorder and developing MS was not significant.
Conclusion: We found a strong positive association between MS and bipolar disorder and depression that could not be explained by genetic liability. The unexpected negative association between MS and schizophrenia might be spurious or indicate possible protective mechanisms that warrant further exploration.