She is suffering from senile dementia.

她受老年痴呆症折磨。

《柯林斯英汉双解大词典》

Suffering from dementia, she had apparently wandered off and gotten lost.

她患有老年痴呆症，很明显是由于擅自出走而走失的。

youdao

For example, physicians have long known that suffering a stroke, in which blood flow to the brain has been interrupted by a clot or a hemorrhage, can lead to dementia.

例如，医生们早就知道的，因流向大脑的血液出现梗塞或脑溢血造成的中风也可能会导致痴呆。

youdao

The government say they are addressing current dementia services and looking at how they can effectively deal with the projected growth in the number of people suffering with dementia over the next 20 years.

BBC: Statement on the dementia plan

Ms. Baral had been suffering from dementia.

FORBES: 5 Neglected Tax Developments of 2011

They also explained how people missing in the mountains were usually lost or injured, whereas these semi-urban searches were often for people suffering from dementia, feeling suicidal, or young children - all factors that could effect how the missing person acts.

BBC: Rescuers tackle urban landscape