A 70-year-old male visits his GP with his concerned wife. She reports her husband has not been himself for the last 9 months and has slowly withdrawn from his hobbies. She has noticed that he is more forgetful and sometimes struggles to find the right words. This has progressively worsened over the last 4 months. She also tells you that he has trouble paying attention to the tv programmes he used to love. He is also having problems with urine incontinence. He has a PMHx of HTN, TIA, diabetes and carpal tunnel. He has never smoked. The most likely diagnosis is: