Cognitive Profiles and Subtypes of Patients with Mild Cognitive Impairment: Data from a Clinical Follow-Up Study 359
ties in planning or decision making, may have been con-
sidered important in addition to memory impairment.
Furthermore, this study included cases where patients’
guardians or informants reported memory impairment
even without subjective memory complaints from the
patients, which resulted in a higher rate of MCI cases
relative to those of other studies.
During the 24 weeks follow-up period, all patients of
MCI with each subtype of MCI showed significant im-
provements in cognitive fun ction on the to tal score of the
SNSB-D compared with the baseline assessment. In the
major cognitive items of the SNSB-D, there was signifi-
cant change between the initial and the follow-up as-
sessments in the domains of language, memory and the
frontal/executive function in all subtypes of MCI. This
result is probably due to a relatively large number of pa-
tients with high MMSE scores and mild stag e of patients
being included, and learning effect may have resulted
during the relatively short follow-up period. The condi-
tion of depression may also have had an influence on the
test scores, given that the patients with high depression
scores in the initial tests sh owed improvement in the fol-
Our study showed that two MCI patients (2.4%) pro-
gressed to Alzheimer’s disease; their subtype during the
initial test was aMCI-m. No patient progressed to other
types of dementia other than Alzheimer’s disease. A
3-year follow-up research study reported that rates of
conversion to Alzheimer’s disease for the MCI subtypes
were 38% for amnestic MCI , 20% for non-amnestic MCI
and 16% for amnestic multiple domain MCI . The
other long-term follow-up study revealed a conversion
rate to AD at 49% for amnestic MCI and 27% for non-
amnestic MCI . Our study did not show in-depth con-
version rates due to a shorter follow-up period. However,
our results show a tendency for progression to AD from
amnestic MCI rather than non-amnestic MCI.
We identified some shortcomings in our study. First,
although it was a prospective follow-up study, we did
observe changes in the MCI patients’ subtypes and their
cognitive functions during the short period of 24 weeks,
therefore making it difficult to form a precise evaluation
of the patients’ disease progression or an estimation of
the annual rate of conversion from MCI to dementia.
Second, the number of patients in each subtype was un-
evenly distributed, making it difficult to determine true
statistical significance. Also, differences in levels of
apolipoprotein E4 were not obtained from all patients,
nor the analysis of differences in MCI in accordance with
the existence or non-existence of cerebrovascular lesions,
such as white matter changes or lacun ar infarction.
In conclusion, we were able to verify that the SNSB-D
is a useful tool to classify MCI subtypes and follow their
progression in detail, suggesting that the routine classifi-
cation of MCI into subtypes and observation of progres-
sion may be conducive to predicting a transition of MCI
to Alzheimer’s disease or other types of dementia. In our
study, aMCI-m was the most common subtype among
the four subtypes of MCI, and its rate of conversion into
Alzheimer’s disease was statistically significant. For a
more comprehensive investigation, it will be necessary to
perform further prospective multi-center research for a
period of a few years, with many hundreds of patients as
subjects, in region-based cohort studies as well as hospi-
tal-based cohort studies.
This study was supported by a grant from the Korea
Healthcare Technology R&D Project, Ministry of Health
and Welfare, Republic of Korea (A102065) and Eisai
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