After a TIA, dementia was far more common than recurrent stroke, and its risk stayed raised for 20 years

Design

Population-wide matched cohort, linked administrative data

Population

113,081 adults after first TIA in Ontario, with matched controls and stroke patients

Primary outcome

Incident dementia over up to 20 years

Effect

HR 1.34 (1.31 to 1.36) overall; 1.75 (1.66 to 1.85) in year one; 19.3% diagnosed

A population-wide matched cohort in Neurology (23 September 2026) used Ontario health data from 2002 to 2022 to follow 113,081 adults after a first TIA (mean age 70), from 90 days after the event, against matched population controls and people with a first stroke. Those with prior dementia or stroke were excluded.

Dementia was diagnosed in 19.3% over a mean of seven years — 2.71 against 2.03 per 100 person-years in controls. The hazard was highest in the first year (HR 1.75, 95% CI 1.66 to 1.85) and remained raised over 20 years (overall HR 1.34, 1.31 to 1.36). Early on, dementia risk was lower than after stroke (1-year HR 0.67), but the two converged after five years. Dementia was much more frequent than new stroke, and adjusting for intervening stroke changed little.

This is administrative data, and some 'TIAs' will have been mimics or small strokes; diagnosis coding of dementia is imperfect. But the size and consistency of the association are hard to dismiss.

TIA follow-up typically focuses on preventing the next stroke. This suggests it should also include cognition.

• Record a baseline cognitive screen at TIA follow-up
• Tell patients and families that memory problems after TIA are common and worth reporting
• Re-screen cognition at later reviews, not just in the first year
• Treat vascular risk factors aggressively — the same targets serve stroke and dementia prevention
• Do not assume a TIA with full recovery leaves no lasting consequence

Why it matters

It reframes TIA as a cognitive as well as a stroke-risk event, which most TIA pathways do not yet reflect.

Don't overread it

This is an association in administrative data; it does not show that any intervention after TIA prevents dementia.

The statistics, in plain English

A hazard ratio of 1.34 means dementia occurred about a third more often in people after TIA than in similar people without one, at any given time. The 1.75 figure applies to the first year, when some cases may be dementia already present but unrecognised at the time of the TIA.

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