Despite the current diagnostic criteria suggesting no functional impairment, our results indicate that patients with MCI experience mild functional deficits, including deficits in modified IADLs and ADLs; these vary according to MCI subtype. Amnestic patients are more likely to experience problems with remembering lists and recalling recent events, whereas nonamnestic patients experience more difficulty with ADLs such as eating and continence. Although we are uncertain of the clinical significance of these findings, we hypothesize that those with nonamnestic MCI, especially with executive impairment, experience greater subclinical white matter disease, leading to more problems with tasks like eating and continence. These results suggest that it may be useful and necessary to evaluate function in patients with MCI to determine whether and the extent to which functional deficits exist.
Our results support previous studies showing that patients with MCI experience more functional impairment than normal healthy controls, and that the functional deficits typically involve memory-related tasks.6–8
Our results contradict another study that found no significant distinction in the functional impairment experienced by amnestic and nonamnestic patients, but this discrepancy could be because of differences in study population and sample size.6
These findings add to current literature because they show that patients with MCI are also experiencing minor deficits in ADLs.
Our findings demonstrate that amnestic patients experience deficits in modified IADLs. Importantly, some of the IADLs measured on the BRDRS are not traditional because they ask questions of memory; these were the impairments experienced most by patients with amnestic MCI. Whether this translates to actual worse functioning in performing related tasks, such as shopping for groceries, is less clear. Conversely, nonamnestic patients experience deficits with basic ADLs. These differences may be explained by different neural structures being affected in nonamnestic as compared with those with amnestic MCI. For example, those patients experiencing executive domain problems most likely have neuropathology in the frontal lobes, whereas those with amnestic MCI have it in hippocampal and entorhinal cortex.12, 13
As mentioned previously, functional deficits in patients with MCI may have gone unrecognized in patients with MCI owing to various reasons such as subclinical symptoms and inaccurate reporting from patients and caregivers.3–5
It has been shown that patients with MCI are not able to provide objective ratings of their own functional impairments, and informant reports of impairment or objective clinical assessments are necessary.5, 14
In an attempt to overcome these difficulties, obtaining information from both patients and caregiver informants on functional status of the patient with MCI will be useful.
There are several strengths to this study including the multidisciplinary evaluation and extensive cognitive testing used to reach a diagnosis of MCI. Furthermore, the sample size is larger than some of the other studies that have investigated functional impairment in patients with MCI, offering more statistical power. Some limitations should also be considered, such as the study population. The ARCCs are academically affiliated hospitals where patients are examined by specialists, thus results may not be generalizable to patients outside of this setting. Lack of functional impairment is used in the MCI diagnostic criteria, thus the BRDRS was one component used in formulating a final MCI diagnosis, which is a limitation. However, we found it interesting that despite this, there was still noticeable functional impairment in the patients with MCI and a distinct difference between patients with amnestic and those with nonamnestic MCI. This was a cross-sectional cohort study, thus we were unable to address causality. Finally, not all traditional IADLs were assessed and some that were assessed included memory-related tasks.
Patients with MCI experience functional deficits, which differ by subtype of MCI. Because patients with MCI who have more functional impairment may be more likely to progress to dementia, it is critical to fully understand and diagnose functional deficits.15
On the basis of this evidence, in combination with previous studies, the diagnostic criteria for MCI need to be reexamined, and a revision to include the minimal functional impairment should be considered. Future studies should continue to investigate to what extent function is impaired in these patients or whether they type of functional impairment predicts the type of dementia.