A new study suggests that older people displaying criminal behaviors might be showing some early signs of dementia or other neurodegenerative diseases.

Madeleine Liljegren, M.D., of Lund University, Sweden, Georges Naasan, M.D., of the University of California, San Francisco and their colleagues wanted to determine why some older people are displaying criminal behaviors for the first time. The researchers presume that this might be because their brains are being damaged by dementia.

The researchers looked at the medical records of 2,397 patients with dementia-like disorders between 1999 and 2012. Twenty-three percent of the participants had Alzheimer's disease, seven percent had behavioral variant of frontotemporal dementia (bvFTD, linked to personality changes), four percent showed language declines and one percent had Huntington disease.

Initial analysis showed that 204 patients or almost nine percent had committed criminal violations after diagnosis of their dementing disorder. Those with Alzheimer's disease are the least likely to commit crimes at seven percent compared to those with the dementia related to personality changes that had the most at 37 percent. These activities include theft, traffic violations, sexual advances, trespassing and public urination.

"The findings from this study suggest that individuals who care for middle-aged and elderly patients need to be vigilant in the diagnosis of degenerative conditions when behavior begins to deviate from the patient's norm and work hard to protect these individuals when they end up in legal settings," the authors wrote in a press release.

The findings of the study echoed the results of earlier studies.

"We were confirming what we knew before, but also adding a sort of comparative flavor as to the differences between people with frontal types of dementia and other types of dementia," said Dr Naasan to Medscape Medical News.

The researchers admitted that their study has some limitations as they only based their findings on the patients who visited their clinic and that they weren't certain how much crime was committed due to dementia.

This study was published in the Jan. 5 issue of JAMA Neurology.