The study of language disruption in dementia aimed at individuating which features correlate with the progression of cognitive impairment is a growing area in computational linguistic research. Still, it needs a further development in analyzing some discourse phenomena that also undergo deterioration, and can help expand our understanding of dementia-related speech and refine automatic tools. This paper explores the discourse property of cohesion by investigating three types of cohesive devices: reference, lexical iteration, and connectives. Ten features related to these categories have been defined and automatically extracted from an Italian corpus of semi-spontaneous speech collected from dementia patients and healthy controls. Some of the designed features have proven significant for the binary classification of the two groups and further quantitative analysis highlight interesting differences in the use of cohesive devices, that seem to be associated with cognitive decline.