Spontaneous speech rate in patients with mild cognitive impairment and early stage Alzheimer's disease

In normal aging population annual conversion rate to Alzheimer's disease (AD) ranges from 0.17% to 3.86%, while in MCI it is higher ranging between 6 and 40%. Although several language studies try to detect the differences between MCI and early stage AD (eAD), the results are still controversial. The objectives of current investigation are to determine speech rate of eAD and MCI and to search if there are any contributing factors that could differentiate MCI from eAD. Nine patients with MCI, 11 eAD, 8 mild-to-moderate AD and 6 SMI without dysarthria were recruited. For the assessment, speech production of all participants was digitally recorded using a simple picture description and conversation. The confrontation naming ability and frontal/executive functions were also assessed. Several speech factors such as total speech rate, articulation rate, median pause duration, total pause rate were measured. A correct information unit (CIU) method was used to calculate information efficiency in the picture description. Group differences were analyzed using ANCOVA. In the picture description task, the total speech and articulation rate were not different in all subgroups, however, the early and mild-to-moderate AD showed longer pause than the MCI and SMI. Early AD revealed a larger amount of pause rate than MCI and SMI. While eAD explained effectively a simple picture as MCI, mild-to-moderate AD poorly performed it compared to MCI and SMI. Statistically significant correlations were noted between pause median and K-BNT, between pause median and frontal/executive functions, and between CIU and frontal/executive functions. In conversation, we could not find any significant differences in speech rate measures among 4 subgroups. Our results show that there are differences between MCI and eAD in some speech rate features. Compared to MCI, longer pause duration and larger total pause rate were noted in AD group. Semantic degradation or frontal/executive dysfunctions such as organization failure or retrieval deficit might influence response time in spontaneous speech even in the early stage of dementia. We suggest that paying attention to speech rate such as pauses could be of clinical significance in discriminating eAD from MCI.