IMAGINE for a moment, that you are so short of breath that you seek advice from your GP, whose vague diagnosis is "major breathlessness".
"You wouldn't feel particularly informed," says Professor Gordon Parker from UNSW and Black Dog Institute. "You would want to know whether your breathlessness was due to pneumonia or asthma or pulmonary embolism because you would then know that you would get the salient and specific therapy."
Parker uses the same analogy with diabetes – knowing whether it is type 1 or type 2 is important given the stark differences in cause and treatment. Yet, depression is currently classified as "major" or "minor" with no recognition in diagnoses or distinction in treatment between varying causes and types.
A new review paper, published in the journal Brain, Behaviour, and Immunity, calls for depression to be reclassified.
"We argue that depression is not a single disease, it is a heterogeneous syndrome, with patients differing remarkably in symptom profile, pathophysiology and treatment responsiveness," says co-author Severi Luoto, a PhD candidate in evolutionary psychology at the University of Auckland.
"The evidence that major depressive disorder is a group of separate syndromes comes from the observations that patients not only have many hundreds of unique symptom profiles, but many of the symptoms often have opposite features such as insomnia or hypersomnia, or an increase or decrease in appetite."
Parker says the way depression is defined is "a big issue" in psychiatry.
In 1980 the DSM (the Diagnostic and Statistical Manual of Mental Disorders published by the American Psychiatric Association) changed the depression disorders classification to fall under the one umbrella of major depression. It reflected the view that there was only one type of depression that varied along a dimension from mild to severe.
"The consequences of that were major because up until the 1950s when the first antidepressant was discovered, the lifetime rate of clinical depression was thought to be about 2 per cent – maximum 5 per cent," Parker explains.
"When they brought in this concept of 'major depression' with a low cut-off bar, something between 25 and 30 per cent of people in western countries have 'major depression' over their lifetime. Another 30 or 40 per cent have 'minor depression' and it blew the bars out in clinical depressions and made it fairly meaningless because clinical depression then became a lifetime expectancy."
According to Beyond Blue, it's estimated that 45 per cent of Australians will experience a mental health condition in their lifetime, with about one million adults experiencing depression in any one year.
With the reclassification of depression, the company that created the first antidepressant went from not having enough people to warrant developing the drug to having an abundance.
"The drug companies, in my view, did not drive this model, but they took advantage of it," Parker says.
The problem is that antidepressants don't work for every type of depression, yet have been liberally prescribed under the umbrella model.
"There have been multiple studies looking at treatment for 'major depression' and it doesn't matter whether you look at old antidepressants, newer antidepressants, psychotherapy, you look at counselling – every treatment comes out as comparable.To my mind, that reflects the problem in homogenising multiple differing subtypes," Parker says.
"Let me give you another analogy. Let's imagine you invent a super-duper treatment for asthma but you don't test against people with asthma, you test against people who have 'major breathlessness' – only 5 per cent of that group have got asthma, then your active drug may not differentiate from placebo because it's been washed out with all the noise."
Antidepressants, Parker says, work for those with "melancholic" or biological depression.
"Essentially, that is the disease which runs in families, episodes come on out of the blue and it doesn't respond to psychotherapy," Parker explains.
On the other hand, a whole range of "non-melancholic" depressions, which could be caused when vulnerable personality types are exposed to environmental triggers or could result from traumatic life events, may better treated with psychotherapy.
"The art of being a good clinician is to formulate when a patient walks in with depression and say 'why is this person depressed at this particular time and what type of depression do they have?'
"That has been my key argument for a long time. It's not a one-size fits all argument. It's horses for courses."
Despite Parker leading a call to reclassify the DSM-5 in 2012, the "unitary" model of depression remains along with the division in the psychiatric community.
The main argument for not changing the classification is that the evidence for making such a big change is still lacking. Although it is"imperfect", there is merit in its simplicity and it's the best we've got based on the current research, they say.
"We know enough to know that the traditional DSM approach is obsolete, but we do not know enough to articulate the paradigm shift we know will be necessary," wrote Jan Fawcett, a professor in the department of psychiatry at the University of New Mexico's School of Medicine.
How the debate is resolved remains to be seen, but it highlights the complexities of the human brain and the complexities of mood disorders that even the experts are still learning about.
Even those calling for subtypes are not all in agreeance.
The authors of the new paper argue that depression subtypes are induced by: 1) infection, 2) long-term stress, 3) loneliness, 4) traumatic experience, 5) hierarchy conflict, 6) grief, 7) romantic rejection, 8) post-partum events, 9) the season, 10) chemicals, 11) somatic diseases and 12) starvation.
Parker, while agreeing with their main argument against an umbrella model, disagrees with their suggestions, saying: "I think they have too many different precipitants. I would be very surprised if the different precipitants shaped the different subtypes."
Parker says the psychiatric community needs to figure our how to stop people from getting "over-treated".
"The concept of joining all depression disorders into a single diagnosis and calling it something like 'major depression' ... is not informative at any level. It is no more informative than a concept like 'major breathlessness'," Parker reiterates. "We need specific subtyping diagnoses, as occurs in medicine, so a treating doctor can give a more precise diagnosis and ... a cause-specific management plan."
