Black Dog Institute’s Model of Depression embraced by the Psychiatrists at The Lawson Clinic
“The concept of ‘major depression’ has led to sterility in depression research and clinical practice, and there is a need for a paradigm shift in modelling and classifying the depressive disorders” – Professor Gordon Parker
The North American DSM-IV classification system views depression as a single entity and differentiates conditions based on severity and duration. Major depression – severe and present for more than two weeks, and dysthymia – moderate and present for more than two years. The Black Dog Institute believes this severity-based approach is impractical both in theory and practice and is rarely used in other disciplines.
An alternative hierarchical model has been developed at the Black Dog Institute (which is applied by the psychiatrists at The Lawson Clinic) that assumes there are three subtypes to depression. There are two distinct categories of essentially biological conditions (melancholic and psychotic depression) which have identifiable defining features, and a residual group of quite varying conditions (non-melancholic depression). This residual group is therefore associated with varying presentations reflecting the contribution of life event stressors and personality style.
In all three subtypes there is a mood disorder component. The key features include a depressed mood, decline in self esteem, self-criticism, the mood state is present for at least 2 weeks and causes social impairment. The key feature which defines melancholic depression is observable psychomotor disturbance (PMD) – e.g. retardation and/or agitation together with a cognitive processing difficulty. In psychotic depression, the PMD is generally more severe and combined with psychotic features such as delusions, hallucinations and/or over-valued ideas.
Based on research and clinical findings in response to treatment, we suggest that the non-melancholic depressions are principally underpinned by serotonergic dysfunction (affecting sleep, appetite, anxiety, irritability, and mood). For the specific features (such as psychomotor change) evident in melancholic depression and the psychotic features in psychotic depression, there are additional noradrenergic and dopaminergic contributions respectively.
An understanding of the hierarchical model of depression helps to make logical and appropriate treatment decisions.
Hierarchical Model of Depression
The prevalence of each type of depressive disorder generally seen in general practice is:
- Non-melancholic – Common > 90 %
- Melancholic – Less common 2-10 %
- Psychotic – Rare 1-2 %
Model of Depression
Typically, two main profiles are seen in general practice:
- Depressions which are less common but nonetheless potentially fatal, such as psychotic, melancholic and bipolar depression. On DSM-IV criteria, these are usually lumped together as ‘moderate’ or ‘severe’ Major Depression; and
- Depressions here termed ‘non-melancholic’ depression, are more common in the community and include a number of subtypes which reflect underlying personality styles. On DSM-IV criteria, these are usually all lumped together as ‘mild’ or ‘moderate’ Major Depression.
It is important to note however, that non-melancholic depression as defined in our hierarchical model is a qualitative definition and can present at all levels of severity.
Bipolar I & Bipolar II
The classification of the different types of bipolar disorder has been an issue of debate for some time. Increasingly, in some parts of the world there has been a move to the development of more categories or subtypes of bipolar disorder. Bipolar III, for example, has been defined to mean where a person experiences a hypomanic or manic switch after receiving an antidepressant. The principal types (bipolar I and bipolar II) may be separate sub-types or differ merely dimensionally (e.g. by severity or duration), with the term ‘bipolar spectrum’ assuming dimensional differences.
Why making the distinction is important come down to the implications for treatment. In bipolar I disorder, the mood stabilisers (especially the gold standard, lithium) are considered to be the mainstay of treatment. The role of the mood stabilisers in bipolar II disorder is less clear and up for debate, especially as new antidepressants and atypical antipsychotics have come on the market. There is an increasing interest in this area and more trials are currently underway. These will hopefully clarify whether each condition should be similarly treated.
Bipolar I Disorder
Bipolar I disorder is defined as being present if the person experiences one or more lifetime episodes of mania and usually episodes of depression. The severity and duration of episodes are often severe and may result in hospitalisation.
Bipolar II Disorder
Bipolar II disorder is defined as being present if the person experiences episodes of both hypomania and depression but no manic episodes. The severity of the highs does not lead to hospitalisation.
Six key features of mania and hypomania
What separates normal ‘happiness’ from the euphoria or elevation, which is seen in mania and hypomania? Research at the Black Dog Institute has identified six principal features that appear to make this distinction. These features are:
- High energy levels
- Positive mood
- Inappropriate behaviour
- Mystical experiences.
As noted, in mania, these experiences are more extreme and severe. Mystical experiences can reach delusional intensity with the development of other psychotic symptoms. The high levels of energy reach manic excitement; the patient is unable to sleep, thoughts and speech are so fast as to be unintelligible. Inappropriate behaviour can place the individual or others at risk, especially if associated with intense irritability and delusional beliefs (e.g. persecutory delusions that someone is after them, or grandiose delusions that they have the power of flight).
The depression experienced by sufferers of bipolar disorder is equally severe for people with bipolar I as for people with bipolar II. Some recent studies have reported that depression can be both more frequent and more chronic in the case of people with bipolar II than with bipolar I. There has also been found to be a comparable suicide risk between the two subtypes.
Thus, definitional differences are not always associated with clear functional differences.