In this study, we compared the cognitive profiles in DLB and PDD patients using a broad neuropsychological battery. Most of the measures showed similar patterns globally, with a trend for poorer performance in the DLB group. These results are consistent with previous studies1,2,3
and suggest a common pathological process underlying the diseases.
However, despite the small sample size and large intragroup variability of results suggesting heterogeneous patterns, we observed some significant differences in cognitive patterns of DLB compared with PDD patients.
Firstly, patients in the DLB group had poorer performances in orientation subtests than PDD patients. As DLB is sometimes defined as a chronic confusional syndrome,23
this result is not surprising.
Secondly, performances were poorer in the DLB group in the Trail Making Test‐A test and in the reading of names of colours in the Stroop Test (ie, initial phases of each test). These results could suggest that DLB patients require more time than PDD patients to learn tasks, but once learned, tasks are performed to a similar standard by both groups.
The major result was the different pattern of memory impairment on the DMS‐48 test between PDD and DLB patients. This recently introduced test explores visual object recognition memory.24
Performances were more impaired in DLB patients (both in immediate and delayed recognition) than in the PDD group, suggesting the following hypotheses. As encoding is not controlled in the DMS‐48 test, DLB patients could have more severe attentional disturbances than PDD patients, resulting in less immediate recognition. Just as the immediate recognition score was low, delayed recognition was also impaired. We can also hypothesise that DLB patients have more functional alterations in temporal regions (in particular the perirhinal cortex that is crucial in visual object recognition memory).24
To our knowledge, ours is the first study describing differences in neuropsychological testing between PDD and DLB in terms of memory.
Few studies comparing cognitive functions in PDD and DLB have been published. Aarsland et al2
and Downes et al25
showed that executive functions in patients with mild DLB were more impaired than in patients with mild PDD. Ballard et al
compared cognitive reaction times in several neurodegenerative pathologies but did not observe differences between PDD and DLB.1
Noe et al
did not observe differences in memory using the Selective Reminding Test, or in a battery assessing a broad range of cognitive functions.3
Hence our study is the first to investigate DMS‐48 in DLB and PDD.
Our findings must be consolidated in future studies, with a larger sample of patients. Nevertheless, based on our results, neuropsychological testing, especially DMS‐48, appears to be useful in characterising DLB and PDD.