[rdmirza]

The main concern here (and most observational studies) is confounding by indication. Specifically, the same reason some people got hydroxychloroquine as opposed methotrexate is the same reason you see differences in the outcome. In this case there’s plausible confounding that needs to be addressed before any conclusion like the title could be drawn.

Generally hydroxychloroquine is used in mild rheumatoid, whereas methotrexate is used in moderate-severe disease.

Inflammation in rheumatoid (and other inflammatory diseases) contribute to atherosclerosis and plaque buildup. Rheumatoid increases the risk of coronary disease by 1.5-2x.

That difference alone could account for the difference in dementia, particularly vascular dementia.