A Sense of Humour: Classifying Mental Illnesses

August 13, 2007 at 11:18 am 3 comments

Depression was, up until the 19th Century, seen as an excess of the melancholic humour. Mania, too much of the sanguine humour. Psychosis Choleric. Catatonia: Phlegmatic. And let’s be clear, these humours of the body weren’t metaphorical, we’re talking about black bile, blood, yellow bile and phlegm.

It’s one system of categorisation. Not a particularly useful one, but a system nevertheless. You know the rest of the story in its vague outlines: Madness, asylums, medicalisation, etc. etc. Leading to the development of the modern categories of madness, as outlined in the DSM and other similar manuals.

Categories are not real. They’re ways of organising information by specific properties. I’m going to take a quick detour via skin disease, we’ll get back to madness in a minute. Let’s take an example: Melanomas are a type of skin cancer. Melanomas are real things; in simple terms they’re a collection of skin cells (melanocytes, to be exact) that grow and divide uncontrollably. The category they’re put into is a way of understanding them. The international classification of diseases (ICD) categorises them as:

Neoplasms – Malignant Neoplasms – Malignant neoplasms, stated or presumed to be primary, of specified sites, except of lymphoid, haematopoietic and related tissue – Melanoma and other malignant neoplasms of skin.

Each subcategory adds information as it becomes more specific. The most important feature is that they’re neoplasms, the next that they’re malignant, and so on. This is useful, because it tells us that malignant melanomas can be treated in similar ways to other malignant neoplasms. Other skin diseases – warts for example – are in another category entirely (viral infections characterised by skin and mucous membrane lesions) despite looking superficially similar. What the ICD cares about isn’t looks, but aetiology – the causes behind the disease.

By comparison, a textbook from 1887 (Treatise on Diseases of the Skin, with Special Reference to their Diagnosis and Treatment by Thomas McCall Anderson) would have classified melanomas like so:

Diseases of the Skin – Organic Affections – New Formations – Epithelioma

For Anderson, the important thing is that it’s a disease of the skin, organic rather than function and involves a new formation rather than an inflammation or haemmorrhage. Warts are in the same category, because they present in the same way.

Both categorisations are designed for a particular use. Anderson’s classification works for a 19th century doctor, trying to diagnose skin diseases; the ICD works for modern medicine. And they are both based on assumptions about what knowledge is pertinent for a given use. All categorical systems do this: That’s what they’re for. The quality of a categorical system depends on the quality of the knowledge that informs it and the appropriateness of the use it’s put to.

I’m done with skin diseases: Back to madness. The ICD classification for bipolar disorder goes:

Mental and behavioural disorders – Mood [affective] disorders – Bipolar affective disorder

Which of the two classifications does this most look like? It’s nothing like the etiological classification for melanoma. The knowledge that informs it is, like Thomas McCall Anderson’s classification, based on what it looks like, not how it’s caused. Which is fair enough, because mental illnesses are famed for having unknown causes. We don’t know how they work, so it would be unreasonable to expect them to be classified that way.

Consider how the categorisation of melanoma allows us to generalise about them: All kinds of abnormal growths (neoplasms) have similar causes: Specific kinds of cells proliferating in an abnormal way. Malignant neoplasms have similar causes: Genes going wrong, which causes the abnormal proliferation of cells. All melanomas have similar causes: Genes going wrong in melanocytes, causing an abnormal proliferation of cells.

The categorisation of mental illnesses does not allow us to do the same thing: Do bipolar disorder and unipolar depression have similar causes? Who knows? For that matter is every case of bipolar disorder caused by the same thing? No clue.

Problems occur when people try to use a 19th century classification as if it were 21st century. Classifications are only as useful as the use they’re put to. Strict diagnostic criteria for malignant melanomas are a good thing. They can look like warts, but a quick application of salicylic acid isn’t going to help. Nor would you want chemotherapy for a verucca. Strict diagnostic criteria for mental disorders are nonsensical: They aren’t informed by the kind of knowledge that can distinguish between conditions that look the same, but present differently. Putting elaborate structures in place to hide this fact isn’t helpful: It informs neither diagnosis nor treatment.

To put it simply: All depressed people are probably not depressed in the same way. We cannot generalise about how depressed people should be treated because when we say “depression” we’re probably referring to a class of diseases that look the same, but have different causes. The same applies to every other mental illness. Most treatments for depression are only slightly effective when measured across a random sample of depressed people; one type of treatment may work for one depressed person, but not another. That’s hardly suprising if they’re different diseases that look the same. No drug is going to be very effective if it’s only targetted at a subset of the people that you think it’s targetted at.

This is why psychiatric treatment is so hit and miss. There’s plenty of psychiatrists who are fully aware of the limitations of their particular branch of medicine, but there’s plenty who aren’t. Diagnosis is fairly subjective, and focusing on sorting people into their correct categories so that you can follow a treatment protocol is useless. The process should be exploratory, like putting a jigsaw together in the dark. You can only feel the edges of the disease based on how it presents: You have to try to fit the edge pieces together to build up a picture of what you’re dealing with and intuit how to treat it.

The categories in the DSM and ICD are better than the four humours, but they’re far more limited and blurry than anyone usually wants to admit. They’re useful, but only when used appropriately and too often they’re not.

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Last Night Distant Suns II

3 Comments Add your own

  • 1. aikaterine  |  August 13, 2007 at 11:30 am

    This was done well.

    “The process should be exploratory, like putting a jigsaw together in the dark. ”

    The best analogy of exploratory that I have run across. I am now stealing it from you.

  • 2. borderlinecrazy  |  August 13, 2007 at 12:11 pm

    Great post! I remain terrified that I was locked up twice according to a 15-minute interview with a 22-year-old armed with a checklist. “She’s borderline and suicidal; better lock her up.” It makes me wonder how many people are walking around receiving the wrong drugs and treatment and being discriminated against because of having the wrong label applied to them.

  • 3. The difficulty of classifying mental illnesses  |  August 17, 2007 at 3:37 pm

    […] This is why psychiatric treatment is so hit and miss. There’s plenty of psychiatrists who are fully aware of the limitations of their particular branch of medicine, but there’s plenty who aren’t. Diagnosis is fairly subjective, and focusing on sorting people into their correct categories so that you can follow a treatment protocol is useless. The process should be exploratory, like putting a jigsaw together in the dark. You can only feel the edges of the disease based on how it presents: You have to try to fit the edge pieces together to build up a picture of what you’re dealing with and intuit how to treat it.” – Read the whole post here […]

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Hi, I'm James. I'm a 26 year old guy from England with bipolar disorder (currently well controlled). I also have a circadian rhythm sleep disorder (not so well controlled). This blog has charted my journey from mental illness, through diagnosis and, recently, into recovery. It's not always easy, but then, what is?

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