Low mood is a sign Sign
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. of depression Depression
A disorder where a person experiences a constant state of sadness and low mood which interferes with their daily activity.. The relationship between depression and dementia is a complicated one. In the days before treatment of dementia was available, the medical literature stressed the need to 'rule out' depression before making a dementia diagnosis Diagnosis
The process by which a physician determines what disease a patient has by studying the patient’s symptoms and medical history and by analyzing any tests performed (blood, urine, brain scans, etc.).. A condition known as 'depressive pseudodementia' was discussed commonly. This was a person who looked as though they had Alzheimer's disease Alzheimer'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., but who responded to treatment with an anti-depressant medication Medication
A compound that is used to treat a disease or illness.. Whether due to wishful thinking, lack of alternatives, or some other reason, 'depressive pseudodementia' was said to be the case for about one person in ten with dementia. As the treatment of Alzheimer's disease became common, depressive pseudodementia was emphasized less.

As it turns out, however, there appears to be something to the idea of depressive pseudodementia. The relationships are complicated. At some level, the simple explanation that being diagnosed with dementia is depressing is true, and accounts for some of the symptoms of low mood. But it is also the case that with Alzheimer's disease (and vascular Vascular
Relating to blood vessels that carry blood throughout the body. dementia, and frontotemporal dementia Frontotemporal dementia
A type of dementia that mainly affects the frontal lobe causing a problem in executive function tasks.) the level of serotonin also falls, as part of the disease process itself. That is why it is sometimes the case that people with mild Alzheimer's disease also benefit from counseling (which itself can raise serotonin levels) and from treatment with an anti-depressant medication.