Can a cognitive test score tell you how much help someone needs with everyday tasks like bathing, shopping, or managing medications? And does that relationship look the same across different types of dementia? A new study from a memory clinic in Japan suggests the answer to both questions may be no — particularly for people living with Lewy body dementia.

The study, published in the journal International Psychogeriatrics, offers a look at how everyday functioning relates to cognitive decline in dementia with Lewy bodies (DLB) and compares it to Alzheimer’s disease (AD) and frontotemporal dementia (FTD). The findings suggest that people with DLB may lose independence in certain everyday tasks earlier than people with AD at a similar level of cognitive decline — a pattern that may reflect the physical and autonomic symptoms common in Lewy body dementia.

What did the researchers do?

The study included 650 patients seen at Kumamoto University Hospital: 524 with AD, 90 with DLB, and 36 with FTD. Cognitive decline was measured using the Mini-Mental State Examination (MMSE), a widely used test scored from 0 to 30, with higher scores reflecting better cognitive performance. Care partners also provided information used to rate two types of daily functioning: basic activities of daily living (ADL) — things like using the bathroom, feeding, dressing, grooming, mobility, and bathing — and instrumental activities of daily living (IADL), which include more complex tasks such as using the telephone, shopping, preparing food, managing housekeeping and laundry, handling transportation, managing medications, and handling finances.

Researchers grouped participants by cognitive decline level and looked at what percentage of people in each disease group could perform each task independently at each level.

What did they find?

Across all three conditions, complex IADL tasks — shopping, food preparation, and medication management — showed low rates of independence even among people with relatively preserved cognition. In the AD group, for example, only about half of people at the higher end of the cognitive range managed shopping or food preparation independently, while simpler tasks like using the telephone or arranging transportation stayed above 90 percent. A similar pattern appeared in the DLB group.

The more distinctive finding, though, was in how DLB compared with AD at similar levels of cognitive decline. Among people with relatively preserved cognition, independence in bathing was about 18 percentage points lower in DLB than in AD, and dressing and handling finances showed gaps of a similar size. Feeding showed a smaller difference of about 7 percentage points. The authors note that these numerical contrasts are consistent with prior findings linking DLB to greater physical and motor difficulties, as well as autonomic dysfunction — changes in body functions like blood pressure regulation and digestion — that could affect self-care and mobility even when cognitive function remains relatively strong.

A note on how cognition was measured

One limitation worth flagging for the LBD community specifically: the MMSE scale, while useful and widely used, is heavily weighted toward memory and other aspects of cognitive decline that are more affected in AD, and is known to be less sensitive to the attention, visuospatial, and executive-function changes that are common early features of Lewy body dementia. This means two people with DLB and AD who score the same on the MMSE may not actually be at a comparable point in their overall cognitive decline — which could partly explain why the study found DLB participants losing daily-living independence at cognitive levels where AD participants were often still managing. The authors themselves did not test this directly, but it's an important caveat when interpreting any MMSE-based comparison involving DLB.

Why this matters

The authors are careful to frame their results as descriptive rather than proof of disease-specific differences — the study did not run formal statistical tests comparing groups, and several subgroups were small. Still, the pattern they describe may be useful in everyday care: complex tasks like shopping, cooking, and medication management can become difficult early in all three conditions, even while cognitive test scores still look relatively strong. For DLB specifically, the authors suggest that mobility, self-care, swallowing, and autonomic symptoms may deserve attention from care teams even when cognition appears comparatively preserved.

For people living with Lewy body dementia and their care partners, this reinforces something many already sense day to day: a cognitive test score doesn't tell the whole story, and it may tell even less of the story in LBD than in some other dementias. A person might do reasonably well on a memory-focused test yet still need meaningful support with practical, everyday tasks — and noticing those gaps early can make it easier to put helpful routines and support systems in place before a crisis arises.

REFERENCE

Hottaa M, Tabirac T, Murata M, et al. (2026) Patterns of ADL and IADL independence across MMSE score ranges in Alzheimer's disease, dementia with Lewy bodies, and frontotemporal dementia: A cross-sectional analysis of a memory-clinic cohort. International Psychogeriatrics, In press. DOI: https://doi.org/10.1016/j.inpsyc.2026.100250.