According to the "Diagnostic and Statistical Manual of Mental Disorders," a diagnosis of major depressive disorder must first rule out alternative possibilities. It is often difficult to differentiate between depression and other disorders because depression tends to co-occur with many other disorders and conditions. The National Institute of Mental Health reported that individuals who abuse drugs or alcohol often experience depression, as well as individuals with medical conditions including diabetes, cancer and heart disease. Additionally, anxiety disorders (e.g. PTSD, OCD) often co-occur with depression. It is important to obtain a thorough history and understanding of the individual's symptoms in order to make the correct diagnosis.
Mood Episodes
A diagnosis of depression requires that an individual experience a major depressive episode, which, as described in the "Diagnostic and Statistical Manual of Mental Disorders," includes depressed mood, weight loss or gain, difficulty sleeping, loss of interest in activities, lack of energy, restlessness or lethargy, trouble concentrating, feelings of guilt or worthlessness, and thoughts of suicide or death. A history of any other type of mood episodes, including a manic, hypomanic, or a mixed (i.e. symptoms of depression and mania) episode suggests a diagnosis of bipolar disorder, rather than depression.
Medical Conditions
As reported by the "Diagnostic and Statistical Manual of Mental Disorders," if it can be determined that the symptoms of depression experienced by the individual are the direct result of a medical condition, than a diagnosis of mood disorder due to a general medical condition is warranted. For example, an individual who suffers from hypothyroidism may experience some of the symptoms of depression, but due to the physical impact of this condition rather than freestanding symptoms of depression.
Substance Use
Individuals using substances may experience mood symptoms similar to depression. The "Diagnostic and Statistical Manual of Mental Disorders" states that persons who are experiencing depressive symptoms due to the use or abuse of a substance should be given the diagnosis of substance-induced mood disorder. For example, an individual going through withdrawal from a substance may experience these symptoms, but would not be diagnosed with depression.
Dysthymic Disorder
Major depression and dysthymic disorder are similar, but differ in severity. The "Diagnostic and Statistical Manual of Mental Disorders" states that individuals with dysthymic disorder experience less-severe depressive symptoms over at least a two-year period, while major depression requires more-severe symptoms over a two-week period. It is important to obtain a full history regarding the severity and onset of symptoms to determine which diagnosis is more fitting.
Schizophrenia and Related Disorders
Symptoms of depression may occur in schizophrenia and other psychotic disorders. The "Diagnostic and Statistical Manual of Mental Disorders" indicates that depression is often seen in schizoaffective disorder; however, the diagnosis requires that the individual experience delusions and hallucinations for two weeks without any mood symptoms. This criterion differentiates between the two. Depressive symptoms are also common in schizophrenia or other psychotic disorders, but are usually part of the disorder and do not require a separate diagnosis.
Dementia
The "Diagnostic and Statistical Manual of Mental Disorders" reports that individuals with dementia experience symptoms including loss of memory, trouble concentrating and disorientation that may look like depression. Medical information and history can help to differentiate between symptoms of dementia and any experience of depression.
References
- "Diagnostic and Statistical Manual of Mental Disorders, 4th edition, text revision"; American Psychiatric Association; 2000
- National Institute of Mental Health: Depression
