Dementia is one of several medical conditions associated with increased rates of depression. Depression in Alzheimer’s disease (AD), the most common form of dementia, occurs in up to 25 percent of patients, and is more frequently diagnosed in patients with mild to moderate AD. Even higher rates of major depression have been linked to dementias associated with Parkinson’s disease and strokes.

Understanding what makes dementia patients particularly susceptible to depression is a focus of current research. One hypothesis is that depression occurs as a psychological reaction to the diagnosis of and limitations brought on by dementia. However, studies have not conclusively shown a correlation between rates of depression in patients with dementia and their awareness or insight into their disease.

A second hypothesis is that physiological causes of dementia may also play a role in the development of depression. Post mortem studies of AD patients have revealed the loss of certain brain cells that are also associated with depression. Also, the high incidence of depression seen after stroke has led researchers to explore how reduced blood flow to the brain that occurs with stroke may cause cellular damage that may also be linked to depression. However research has yet to reveal conclusively that dementia and depression share pathophysiological mechanisms, underscoring the need for further investigation.

Distinguishing symptoms of depression from those of dementia can be challenging, even for clinicians experienced in this area. Diagnosis of depression in a patient with dementia should take the following into account:

• Other medical causes – The first step in the evaluation of an older adult with possible depression, with or without dementia, is to rule out possible medical causes through a careful history, and physical and laboratory evaluations. The patient’s medical history should include a review of medications, and the physical examination should screen for infections, metabolic disorders and malignancy.
• Family and other caregivers– Because dementia is likely to affect a patient’s memory, it is important to involve those close to the patient in providing medical history.
• Symptoms that are unlikely to be mimicked by dementia - Symptoms of dementia including apathy, impaired concentration, and loss of appetite may be difficult to distinguish from similar symptoms of depression. Symptoms more closely associated with depression include feelings of guilt and hopelessness, the belief that one is being punished, and thoughts of death or suicide.
• Personal or family history – Personal history of depression or history of depression in first-degree relatives are both risk factors for developing depression late in life.

A common misconception about persons with dementia and depression is that they are unable to benefit from psychotherapy. A growing body of research disputes that belief. Depending on how far the dementia has progressed, a patient may respond to cognitive-behavioral psychotherapy, and persons with advanced dementia may still benefit from behavior therapy as well as individualized art, music, and recreational therapies. Antidepressant medication may benefit some patients with dementia and depression. Drug therapies come with a unique challenge for these patients: because cognitive impairment can affect medication compliance, there needs to be a system in place to ensure that patients take their medication as prescribed.

Depression can compound the disability experienced by patients with dementia. While diagnosing and treating depression can be challenging in these cases, the effort can be rewarded by improved quality of life for patients. Additional research is needed to identify effective therapies for this increasingly prevalent condition.

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