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Autoimmune disease might be linked to dementia risk

People admitted with autoimmune disease 20% more likely to have subsequent dementia

Louise Prime

Thursday, 02 March 2017

Autoimmune disease might be associated with a small but significantly increased risk of developing dementia, according to the findings of an Oxford-led research team. They said their large, long-term study,* published online today in the Journal of Epidemiology & Community Health, backs up the theory that Alzheimer’s disease (AD) might have an autoimmune component.

It has previously been suggested that autoimmune and inflammatory activity could play a role in the development of dementia, and that Alzheimer’s disease might have an autoimmune component, and researchers from the University of Oxford wanted to find out more. They designed a study to determine whether or not a history of hospital admission for autoimmune disease is associated with an elevated risk of future admission for dementia.

They analysed English hospital admissions data (including day cases) and mortality administrative data, from 1999 to 2012. They constructed cohorts of people admitted to hospital with a wide range of 25 autoimmune diseases (total 1,833,827), and a control cohort (about 7 million), whom they followed forward in time to see if they developed dementia.

They reported that overall, people admitted to hospital with an autoimmune disease were 20% more likely to have a subsequent admission for dementia than those without an admission for an autoimmune disease (rate ratio RR 1.20); where dementia type was specified, the RR was 1.06 for Alzheimer’s disease and 1.28 for vascular dementia.

Of the 25 autoimmune diseases they considered, 18 showed statistically significant positive associations with dementia including conditions as diverse as Addison’s disease (RR 1.48), multiple sclerosis MS (RR 1.97), polyarteritis nodosa (RR 1.43), psoriasis (RR 1.29), systemic lupus erythematosus (RR 1.46) and thyrotoxicosis (RR 1.31). Most of these associations remained significant for five or more years after admission to hospital for autoimmune disease.

They also found that a previous admission with rheumatoid arthritis seemed to protect against AD, but elevated the risk of vascular dementia. As most people with rheumatoid arthritis take non-steroidal anti-inflammatory drugs (NSAIDs) to manage their condition, they said: “Our findings might add circumstantial evidence to the data supporting the hypothesis that NSAIDs protect against AD.”

The researchers said that as their study was observational, they couldn’t infer cause and effect; and the associations they found were significant but small, so their results “should be considered as indicative rather than definitive”. But they pointed out that people admitted to hospital with an autoimmune disease, likely to be those at the severe end of the disease spectrum, did appear to have an elevated risk of dementia, which is consistent with autoimmune disease predisposing to vascular risk and vascular dementia; and also, separately, consistent with the theory that AD might have an autoimmune component.

They concluded: “The associations with vascular dementia may be one component of a broader association between autoimmune diseases and vascular damage. Though findings were significant, effect sizes were small. Clinicians should be aware of the possible coexistence of autoimmune disease and dementia in individuals. Further studies are needed to confirm or refute our findings and to explore possible mechanisms mediating any elevation of risk.”

* Wotton CJ, Goldacre MJ. Associations between specific autoimmune diseases and subsequent dementia: retrospective record-linkage cohort study. UK J Epidemiol Community Health, published online first: 01 March 2017. DOI: 10.1136/jech-2016-207809

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