The history of classification of diseases in medicine is like the history of maps and charts. In the sixteenth century, early map makers in Europe asked ministers of the Church to climb their bell towers and write down everything they could see. Maps were drawn from such recordings.
The development of the magnetic compass allowed more directional accuracy, and made coastal navigation easier. Bearings could be taken from features, and the position of ships calculated. The invention of the sextant permitted the measurement of latitude; that is, distance from the Equator. This was enough to allow Christopher Columbus to cross the Atlantic safely and return home again.
But without the ability to measure longitude, whole areas of charts were left void and marked with the words, ‘There be Monsters here!’ The discovery of how to measure longitude was the major scientific breakthrough of the eighteenth century.
In psychiatry, early attempts at classification were a bit like the ministers climbing their bell towers: all they could do was see their patients, and write down what they saw. And while most of medicine was able to progress through the ‘coastal navigation’ stage, psychiatry had a more difficult task.
In much of medicine, firm objective findings clearly demarcate one disease from another. These findings can be measured—such as a blood test that confirms diabetes, a biopsy that shows a particular type of cancer, or a post-mortem that shows a clot in a coronary artery.
Psychiatric classification has had to operate, as it were, out of sight of land. There are no sharp-edged rocks or islands from which to take a bearing. So, despite the many efforts to identify specific causes of mental illnesses such as schizophrenia, none has been found. Even post-mortem findings, which resolve most diagnostic disputes in medicine, fail to help much in psychiatry.
As a result, maps of psychiatric disorders have been a bit vague, just as charts were before longitude could be measured. But that is changing now, and modern statistics and computer driven research are providing better ways of knowing where in the sea of psychological phenomena we are at a particular time.
Does it matter that there are different depressive sub-types? This is a commonly asked question, and the answer has to be Yes. Just as an accurate position is necessary if you are going to drill for oil in the seabed, or find a good spot for fishing, so too is it very important to know that there are different types of depression.
A pigmented spot of skin may be a freckle or it may be a melanoma. Swollen ankles can reflect either heart failure or a kidney problem. Before doctors could tell the difference, successful diagnosis and therefore treatment was often due to chance.
Such is the risk of viewing depression as a single disorder, and why it is important that the principal sub-types be recognised. Depression used to be thought of as one condition, varying only in severity. Regrettably, many experts and classificatory systems still hold this view. It resembles the markings on the charts before longitude was discovered: ‘There be Misery here.’ Descriptive, but not specific!
The psychiatric classifications of depression that have remained beached in those shoals have provided unhelpful ‘maps’ of depression. Particularly confusing has been the longstanding tendency to classify depression on the basis of severity, descending from ‘severe’ to ‘moderate’ to ‘mild’ and, more recently, as ‘sub-clinical’ and ‘sub-threshold’. This has held back understanding and treatment. For example, in medicine swollen ankles can be ‘severe’, ‘moderate’ or ‘mild’ but these descriptions will not be as important as identifying whether the swelling is due to heart problems or kidney problems. Such is the case in understanding depression.
It is very important to concede that there are different types of depression, as treatments for each type vary in relevance and usefulness—antidepressant medication might be better than psychotherapy for one type of depression, while the converse may hold for another depressive type.
It is also important to concede that while social, psychological, biological and medical conditions can all influence the nature of depression, they do not necessarily provide ‘the explanation’. Even though family tendency to depression, difficulties in childhood, changing cultural trends, and even evolutionary explanations should be considered, such factors are of quite varying relevance to differing depressive ‘types’. Thus, for some people, genetic factors may be the principal ‘cause’ and life stressors of minor relevance; for others, the reverse may hold. And, to have experienced some traumatic event does not, necessarily, make it a ‘cause’ of depression.
There is a famous saying that ‘the beating of tom-toms will always restore the sun after an eclipse’. This reminds us that if two events occur together, we risk concluding that one must have caused the other. Thus, depression might occur for the first time in a menopausal woman—but the menopause may not itself be the cause. Depression may well seem a very logical outcome for someone who has experienced a long sequence of high-level stressors in their life (for example, poor parenting, childhood sexual abuse, the break-up of a marriage and a severe medical illness). While such events may seem a total explanation of the depression, they may have contributed to it only partially or have no relevance at all. The ‘causes’ of depression may therefore be difficult to clarify for a range of reasons. Ideally, professional assessment should clarify the relevance of possible causes and provide an accurate sub-typing diagnosis.
(extracted from) Dealing with Depression: A Commonsense Approach to Mood Disorders y Gordon Parker, published by Allen & Unwin