A 77-year-old man is brought to the hospital by his granddaughter for evaluation of confusion. He has no focal findings and his neuro-imaging studies are normal. Further investigations reveal a urinary tract infection, and the man improves somewhat after treatment, but still exhibits poor judgment and bizarre behavior. Pressing the family for information, the intern unearths a history of 8 years of progressive bizarre behavior. The man has undressed himself and made sexual advances to young female relatives, has urinated in hallways, and pushed food into his mouth with alarming speed. Which of the following is the most likely diagnosis?