Gout Linked to Smaller Brain Volume, Neurodegeneration Risk

Patients with gout may have smaller brain volumes and higher brain iron markers than people without gout, and also be more likely to develop Parkinson's disease, probable essential tremor, and dementia, researchers in the United Kingdom report.

Dr Anya Topiwala

"We were surprised about the regions of the brain affected by gout, several of which are important for motor function. The other intriguing finding was that the risk of dementia amongst gout patients was strongly time-dependent: highest in the first 3 years after their gout diagnosis," lead study author Anya Topiwala, BMBCh, DPhil, said in an interview.

"Our combination of traditional and genetic approaches increases the confidence that gout is causing the brain findings," said Dr. Topiwala, a clinical research fellow and consultant psychiatrist in the Nuffield Department of Population Health at the University of Oxford, England.

"We suggest that clinicians be vigilant for cognitive and motor problems after gout diagnosis, particularly in the early stages," she added.

Links between gout and neurodegenerative diseases debated in earlier studies

Gout, the most common inflammatory arthritis, affects around 1%-4% of people, the authors wrote, with monosodium urate crystal deposits causing acute flares of pain and swelling in joints and periarticular tissues.

Whether and how gout may affect the brain has been debated in the literature. Gout and hyperuricemia have been linked with elevated stroke risk; and although observational studies have linked hyperuricemia with lower dementia risk, especially Alzheimer's disease, Mendelian randomization studies have had conflicting results in Alzheimer's disease.

A novel approach that analyzes brain structure and genetics

Asked to comment on the study, Puja Khanna, MD, MPH, a rheumatologist and clinical associate professor of medicine at the University of Michigan, Ann Arbor, called its novel use of neuroimaging interesting.

Dr Puja Khanna

Dr. Khanna, who was not involved in the study, said she would like to know more about the role that horizontal pleiotropy – one genetic variant having independent effects on multiple traits – plays in this disease process, and about the impact of the antioxidative properties of urate in maintaining neuroprotection.

Dr John FitzGerald

"[The] U.K. Biobank is an excellent database to look at questions of association," John D. FitzGerald, MD, PhD, MPH, MBA, professor and clinical chief of rheumatology at the University of California, Los Angeles, said in an interview.

"This is a fairly rigorous study," added Dr. FitzGerald, also not involved in the study. "While it has lots of strengths," including its large sample size and Mendelian randomization, it also has "abundant weaknesses," he added. "It is largely cross-sectional, with single urate measurement and single brain MRI."

"Causation is the big question," Dr. FitzGerald noted. "Does treating gout (or urate) help prevent dementia or neurodegenerative decline?"

MRI shows brain changes in patients with gout

In what the authors said is the first investigation of neuroimaging markers in patients with gout, they compared differences in gray matter volumes found in the 1,165 participants with gout and the 32,202 controls without gout who had MRI data.

They found no marked sex differences in associations. Urate was inversely linked with global brain volume and with gray and white matter volumes, and gout appeared to age global gray matter by 2 years.

Patients with gout and higher urate showed significant differences in regional gray matter volumes, especially in the cerebellum, pons, and midbrain, as well as subcortical differences in the nucleus accumbens, putamen, and caudate. They also showed significant differences in white matter tract microstructure in the fornix.

Patients with gout were more likely to develop dementia (average hazard ratio [HR] over study = 1.60), especially in the first 3 years after gout diagnosis (HR = 7.40). They were also at higher risk for vascular dementia (average HR = 2.41), compared with all-cause dementia, but not for Alzheimer's disease (average HR = 1.62).

In asymptomatic participants though, urate and dementia were inversely linked (HR = 0.85), with no time dependence.

Gout was linked with higher incidence of Parkinson's disease (HR = 1.43) and probable essential tremor (HR = 6.75). In asymptomatic participants, urate and Parkinson's disease (HR = 0.89), but not probable essential tremor, were inversely linked.

Genetic analyses reinforce MRI results

Using Mendelian randomization estimates, the authors found that genetic links generally reflected their observational findings. Both genetically predicted gout and serum urate were significantly linked with regional gray matter volumes, including cerebellar, midbrain, pons, and brainstem.

They also found significant links with higher magnetic susceptibility in the putamen and caudate, markers of higher iron. But while genetically predicted gout was significantly linked with global gray matter volume, urate was not.

In males, but not in females, urate was positively linked with alcohol intake and lower socioeconomic status.

Dr. Topiwala acknowledged several limitations to the study, writing that "the results from the volunteer participants may not apply to other populations; the cross-sectional serum urate measurements may not reflect chronic exposure; and Parkinson's disease and essential tremor may have been diagnostically confounded."

A novel approach that suggests further related research

"Causation is the big question," Dr. FitzGerald noted. "Does treating gout (or urate) help prevent dementia or neurodegenerative decline?"

Early diagnosis benefits patients

Dr. Khanna and Dr. FitzGerald joined the authors in advising doctors to monitor their gout patients for cognitive and motor symptoms of neurodegenerative disease.

"It is clearly important to pay close attention to the neurologic exam and history in gout, especially because it is a disease of the aging population," Dr. Khanna advised. "Addressing dementia when gout is diagnosed can lead to prompt mitigation strategies that can hugely impact patients."

Dr. Topiwala and her colleagues would like to investigate why the dementia risk was time-dependent. "Is this because of the acute inflammatory response in gout, or could it just be that patients with gout visit their doctors more frequently, so any cognitive problems are picked up sooner?" she asked.

The authors, and Dr. Khanna and Dr. FitzGerald, report no relevant financial relationships. The Wellcome Trust; the U.K. Medical Research Council; the European Commission Horizon 2020 research and innovation program; the British Heart Foundation; the U.S. National Institutes of Health; the Engineering and Physical Sciences Research Council; and the National Institute for Health and Care Research funded the study.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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