Low mood can be seen at any stage of dementia, but is most common in the stage just before the disease is diagnosed, and in the mild stage of Alzheimer's diseaseAlzheimer's disease A neurological disease that affects memory and behaviour. It is characterized by beta-amyloid plaques and neurofibrillary tangles in the brain. There is no known cause but genetics and lifestyle are thought to play a role.. It is also an early signSign In medicine a sign is what a physician finds by examining a patient. For example, a patient with the symptom of pain might have signs of a fast heart rate, a pale face, a clammy touch and tenderness. in vascularVascular Relating to blood vessels that carry blood throughout the body. dementia.