Historically, depression has been thought to be relatively common in Parkinson's Disease; James Parkinson described "melancholia" in his original report of the disease in 1817. Depending on the measures used, the estimated incidence of depression varies from 4% to 75%, although the rates of major depression are thought to be lower, between 7.5% and 16.5% (McDonald et al 2003).
According to the latest edition of the Diagnostic and Statistical Manual (DSM-IV), diagnosis of a major depressive episode requires the following:
At least five of the nine symptoms below for the same two weeks or more, for most of the time almost every day, and this is a change from his/her prior level of functioning. One of the symptoms must be either a) depressed mood, or b) loss of interest.
* Depressed mood. For children and adolescents, this may be irritable mood.
* A significantly reduced level of interest or pleasure in most or all activities. ('Anhedonia')
* A considerable loss or gain of weight (e.g., 5% or more change of weight in a month when not dieting). This may also be an increase or decrease in appetite. For children, they may not gain an expected amount of weight.
* Difficulty falling or staying asleep (insomnia), or sleeping more than usual (hypersomnia).
* Behavior that is agitated or slowed down. Others should be able to observe this.
* Feeling fatigued, or diminished energy.
* Thoughts of worthlessness or extreme guilt (not about being ill).
* Ability to think, concentrate, or make decisions is reduced.
* Frequent thoughts of death or suicide (with or without a specific plan), or attempt of suicide.
The person's symptoms are a cause of great distress or difficulty in functioning at home, work, or other important areas.
The person's symptoms are not caused by substance use (e.g., alcohol, drugs, medication), or a medical disorder.
The person's symptoms are not due to normal grief or bereavement over the death of a loved one, they continue for more than two months, or they include great difficulty in functioning, frequent thoughts of worthlessness, thoughts of suicide, symptoms that are psychotic, or behavior that is slowed down (psychomotor retardation).
To anyone with even a passing knowledge of Parkinson's Disease, there are obvious problems with directly applying the DSM-IV criteria above. For example the following problems may be observed during the normal course of the disease for reasons other than mood: weight loss; difficulty sleeping; slowed-down behavior; feeling fatigued or having diminished energy; poorer ability to think, concentrate of make descisions. However, to complicate things further it may be the case that a patient could be suffering from these symptoms as a direct result or either PD or depression or even both! An ongoing workgroup at the National Institute of Neurological Disease and Stroke (NINDS) recommended that clinicians take an inclusive approach, in other words to rate all symptoms and not try to second-guess whether a symptom was emotional or neurological (McDonald et al 2003).
In clinical practice, the diagnosis of depression in Parkinson's Disease can be pared down to two questions:
1.) Are you depressed, sad, or feeling blue?
2.) Do you enjoy things as much as you used to?
These specific questions are preferable to more vague questions such as "How are you feeling?" or "What's your mood been like?"
McDonald WM, Richard IH, DeLong MR (2003) Prevalence, Etiology, and Treatment of Depression in Parkinson's Disease, Biological Psychiatry 54:363-375