Signature dynamics in Alzheimer's disease

Forensic document examiners are often called upon to opine on the authenticity of handwritten signatures by individuals with diminished mental capacity. Legal arguments surrounding the decisional capacity of an individual with dementia can be found in many cases involving wills, deeds, trusts, and contracts. The purpose of this study was to provide estimates of feature variability derived from dynamic analyses of signatures written by individuals with dementia of the Alzheimer type (AD) compared with age-comparable healthy individuals. Dynamic features of digitally captured signatures were analyzed to test the hypothesis that AD signature features will show greater variability compared with signatures from age-comparable healthy subjects. The study enrolled 69 AD and 74 age comparable healthy subjects. Results revealed four main findings from AD signatures: (1) that the temporal, spatial and fluency characteristics of signature formation did not differ from signatures of healthy writers; (2) variability in dynamic features over a series of repetitive signatures fell within 10% of the natural variation of healthy subjects; (3) there was a significant association between increased dynamic signature feature variability and increased dementia severity for stylized and mixed signatures only; and (4) despite significant decline in cognitive status over a 1-year period, dynamic signature features remained stable. Overall, these results suggest that signature writing is preserved in AD. The association between dementia severity and dynamic feature variability among AD subjects with stylized or mixed signatures warrants further research.