Background: It is not understood why some patients withfrontotemporal dementia (FTD) manifest sociopathic behavior. Objective: To examine the prevalence and characteristics of sociopathic behavior in FTD patients as compared to those with Alzheimer’s disease (AD). Methods and Participants: We surveyed a group of FTD patients and a group of AD patients for sociopathic behavior, evaluated the characteristics surrounding their acts, and compared the groups on neuropsychological tests and functional neuroimaging. Twenty-eight outpatients with FTD (15 men, 13 women; 61.9 ± 7.1 years; Mini-Mental State Examination score 23.6 ± 8.1) were compared with 28 patients with clinically probable AD (13 men, 15 women; 66.1 ± 9.2 years; Mini-Mental State Examination score 21.3 ± 5.3). Main outcome measures included: (a) the prevalence of sociopathic acts; (b) a structured interview; (c) neuropsychological tests including the Frontal Assessment Battery, and (d) clinically obtained positron emission tomography or single photon emission tomography scans. Results: Sixteen (57%) of the FTD patients had sociopathic behavior compared to two (7%) of the AD patients (χ² = 13.84, p < 0.001). Sociopathic acts among FTD patients included unsolicited sexual acts, traffic violations, physical assaults, and other unacceptable behaviors. On interview, the FTD patients with sociopathic acts were aware of their behavior and knew that it was wrong but could not prevent themselves from acting impulsively. They claimed subsequent remorse, but they did not act on it or show concern for the consequences. Among FTD patients with sociopathy, neuropsychological assessment showed impaired motor inhibition, and functional neuroimaging showed right frontotemporal involvement. Conclusion: The results suggest that sociopathy in FTD results from a combination of diminished emotional concern for the consequences of their acts and disinhibition consequent to right frontotemporal dysfunction. In many jurisdictions, FTD patients with sociopathy would not pass legal criteria for ‘not guilty by reason of insanity’.

Frontotemporal dementia (FTD) is