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.
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.
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.
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.
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.
disorders are known to be prevalent in multiple sclerosis (MS).
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.
identified ICD-diagnosed patients with MS (n
= 16,467), bipolar disorder
= 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.
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.
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