The taxonomy of disease

A letter in Nature Reviews Drug Discovery has argued that it is time to reform the taxonomy of disease. The authors are Ismail Kola, head of a pharmaceutics company, and Sir John Bell, Regius Professor at Oxford.

The taxonomy of disease (technically called nosology) is an old one. Of course the Greeks, notably Galen, had their version, and in the 17th century it was a hot topic as well. The problem seems to be that there is a conflict between the phenomenology of disease, and the etiology. That is, we classify on a mixture of what seems to us to appear as a single thing, and on the basis of what we know about causes.

In my forthcoming book with Malte Ebach on Natural Classification, we term the former classification by analogy and the latter classification by homology, using the biological terms as general tags. Classifying natural phenomena based on our dispositions and predilections ultimately tells us mostly about how we react to stimuli. Classifying on the basis of known causes allows us to properly “cut nature at its joints”. But we do not have direct access to causes before we achieve successful theory and modelling, so instead we have to deal with shared properties.

And here is the conundrum. Which properties will tell us about the world, and which about ourselves? The answer is that we do not know, to begin with. Kola and Bell use a number of examples and approaches to suggest how to reform nosology: nearly all of them involve the identification of molecular and genomic pathways in order to find therapies. This may be a useful initial step; but if we take molecular biology to be primary we may be begging some questions.

The authors mention the new version of the DSM, and it is a salutary lesson in the failure to distinguish between phenomenology and etiology. Initially, I am told by Dominic Murphy at the University of Sydney, who specialises in this topic, the DSM was largely based on (largely Freudian) phenomenology with the hope that these categories of mental disorders would be replaced with more biological causal types over time. Instead what happened was that as etiologies were discovered they got added, but that phenomenological classes were also added, mostly because there was a need for a diagnosis that could attract government support either for researchers or patients. Such “diseases” as “autism spectrum disorder” or ASD are heterogeneous grab bags of phenomenal behaviours that seem like each other. Anyone who has a child who falls under that category knows how ridiculous the ASD class is. DSM-V will collapse all variations such as Asperger’s Syndrome into that one class. [Use of the rider "syndrome" in nosology is a fine guide to it being a class based on apparent similarities and not any causal criteria.]

Nobody starts investigating a phenomenon in the absence of prior beliefs and experience, so there is nothing wrong with beginning with phenomenal and analogical classifications of this kind. The problem is that medicine seems to be content all too often to rest with them.

10 Comments

Filed under Biology, General Science, Natural Classification, Systematics

10 Responses to The taxonomy of disease

  1. Not that many years ago, the consensus held that many psychiatric disorders were, as they used to say, functional, i.e. that they had causes that were not primarily physical. In those days, even non-Freudian psychotherapy involved a lot of talking. If we’ve decided over the last few years that most or all mental illnesses are physical at root, it is an interesting coincidence that the same period that saw the emptying of insane asylums and the growing reluctance of insurance companies to cover long-term therapies. These days, you have to be independently wealthy to have a functional problem so luckily very few of us have such things. Who can afford to be neurotic?

    I don’t doubt that some of the grab bag of conditions and problems categorized as mental ailments have important physical/chemical causes, though it is perfectly possible that some the brain abnormalities associated with various conditions are consequences rather than causes of disease. After all, however you act or feel, an MRI or PET scan will show something since even normal behavior is caused by neurons and chemicals and what ever’s bothering you, you have a body. What I don’t get is the basis for the assumption that what we’re dealing with is always or usually somatic at root, though I certainly understand how convenient it would be if that assumption were correct.

    Small story: I once cracked up my doctor’s assistant, a lady I’ve known for years. I came in feeling pretty bad, and she asked me what I though I had. “I don’t know,” I replied, “But I hope it’s syphilis. You guys know how to cure that.” But the advantage of determinate physical causes goes beyond the possibility of definitive (and cheap!) therapies. Conditions that do have a specific material cause solve the problem of moving from phenomenological to etiological nosologies. Compare the situation with a disease like MS, which was often dismissed as imaginary before its neurological basis was figured out, and that of chronic fatigue syndrome whose definition fluctuates at the mercy of committees when it isn’t simply considered a trendy form of hypochondria. Of course if some mental diseases are fundamentally ethical in nature or consequences of a particular personal history, they still have causes though their diagnosis and classification will require a different basis.

  2. Jeb

    I had thought I would be avoiding philosophy for a while. I would appear to have underestimated my own capacity for arriving at a stupid idea yet again.

    Look forward to the book with some interest.

    A hot and difficult topic in the late 17th. Robert Boyle’s personal papers reveal a very different position from his published work on medicine, which is more supportive of contemporary practise.

    He was on the outside of medicine but with close ties to key figures.
    Commenting on the territorial preserve of a different profession was an issue he found highly problematic.

  3. bob koepp

    If one’s medical ontology views health in terms of normal functional capacities and disease/pathology in terms of dysfunction, then the taxonomic problem is at least partly resolved. We would need a catalog of the ways in which the parts and processes of a type of organism can be dysfunctional. This seems to me to be the way medical pathologists actually do proceed. Presumably, dysfunctions needn’t have an associated phenomenology, at least not when they are “sub-clinical”. Also, something akin to multiple realizability gets in the way of a straightforward etiological nosology, since the same dysfunction could result from distinct causes.

  4. Hey John, Keep your options open. Perhaps there’s work opportunity available for you with this new direction in the classification of disease. :)

  5. Jeb

    “Don’t become insane but if you do, you must behave as follows…..”

    Anthropological study from New Guinea I dug from my collection looking at temporary forms of madness as cultural play. It lists the taxonomy being argued over by Anthropologists at the time, the writer favours
    ‘wild-man behaviour’.

    It also gives native term used which is yu prim. Term is used for these forms of temporary behaviour and to describe people who are permanently deaf and male.

    Both forms of yu prim would appear to have an entertainment role within local culture.

    http://www.jstor.org/stable/40330070?seq=1

  6. Raving

    the hope that these categories of mental disorders would be replaced with more biological causal types over time

    Things go awry before this juncture.

    The assumption is that the congenital disorders of ADD, BPD, OCD, PDD and others are essentially pathological is false.

    It is easy to suggest that each of these four forms of major thought disorders has a simple and singular functional etiology. These four terms … ADD, BPD, OCD, PDD represent mutually excluding (quasi, meta, ?) phenotypes. They represent independent cognitive methodologies for accomplishing a common and joint cognitive task.

    These four cognitive methodologies are mutually excluding because any single proclivity represents a canalization of habit that requires a lifetime of specialization. No apologies are necessary here. My suggestion is that once a person starts down a specific road for perceiving reality and constructing memories, it becomes a journey of a lifetime. Turning back and going down an alternate methodological path isn’t feasible in the primary meaning of such. Everyone possesses the cognitive anatomy to be a ADD, BPD, OCD, PDD or extra type person. To a certain extent we all use all the methods. Thinking would be difficult, if not impossible without such. Nevertheless and notwithstanding such a proclivity for any single cognitive method over another has such a high affinity or productive consequence that singular specialization (canalization) cannot be avoided.

    Why are ADD, BPD, OCD, PDD called congenital thought disorders?

    There are two intensive reasons. The 1st reason is far and away the greatest hurdle perversely.

    First Reason: It is very difficult to describe the simple and singular functionality of these 4+ cognitive methodologies. There are two sub-reasons

    a) These methodologies are extremely simple and very intense. Their action can be captured and described in a few meager sentences. Once having stated as much, it is well nigh impossible to carry the consideration further. It is too dense …

    This 1st predicament is the main issue. Future posts to this blog will elaborate in this direction.

    b) Medicine concerns itself with pathology. We visit the physician to cure problems. The 4+ thought proclivities are recognized and identified by medical science contingent on pathological phenomenology.

    These 4+ thought proclivities are predominantly functional and extremely effective. As with any method, each approach has it’s limitations, it’s susceptibilities and it’s characteristic breakdown modes.

    Each individual is more than just a thought proclivity. It’s not especially easy for any person to develop effective functional maturity. Failure to succeed in struggle to achieve functionality can lead to complete incapacitation for any person by any method. There are no guarantees.

    How do I prove my conjecture that congenital thought disorders are not that at all? Rather they represent functional and effective, mutually excluding phenotypes.

    Extremely fast supporting evidence:

    a) These thought proclivities are mutually excluding. There is no co-morbidity.

    b) Medicine is unwilling to describe the functional benefit of these cognitive methodologies. They are pathological conditions. Something is broken. That is clearly evident. There is a lack of appreciation of an otherwise functional and effective purpose. I am PERSONALLY able to provide a singular functional and very effective purpose for these phantom cognitive structures. I intend to provide this description in future posts.

    c) Many, if not all of these congenital thought disorders are recognized as possessing a ‘spectrum’ of pathology. There is a spectrum of characteristic breakdown modes to an otherwise singular functional and effective activity.

    Singular functional effectiveness versus ‘spectrum of functionality’

    A simple and singular description of functionality and effectiveness is extremely parsimonious.

    Eighty+ percent of philosophers are autistic. That is not an insult. That is not a dismissive assertion.

    Autistic people have an innate ability and inclination to be rational, logical and perhaps most importantly, autistic people are extremely objective. They have sensibility in detail bias. They represent 1/5 of humanity (5 thought styles split into equal fifths). Most autistic style people are not incompetent. A majority are extremely effective and successful in life.

    I am not autistic. I am an ADD type thinker. I am part of the 80% of humanity which is not naturally out of habit rational, logical or objective.

    In not being autistic, I lack the innate skills of being rational logical and OBJECTIVE. I’m not pedantic. I hate details. I am careless, incoherent, emotional and volatile. I must struggle to do a poor job of being a philosopher, mathematician or physical scientist.

    I do consider myself to be a theoretical biologist. Biology is a domain of natural phenomena where ‘subjectivity’ is everything.

    I admire your interest, your knowledge and your ‘objective’ ability with regard to biological process. That won’t win you any job. You are far more successful than me. I’m not going to stop and get hung up on your ‘objective’ sensibilities. I accept them and appreciate them for what they are and what they can accomplish.

    I’m here to fix the problem with the stupid NT 80% of humanity which isn’t naturally inclined to be rational, logical or objective.

    It is well past time to resolve the ‘mind body’ problem.

    I cannot go much further in elaborating upon the 2nd reason that medicine has blundered by failing to recognize the functional effectiveness of the 4+ congenital thought proclivities. I cannot proceed further because the 1st reason provides the fundamental obstacle.

    Thus I proceed by directing my future posting efforts at describing what objectivity means.

    I’m here because this is the right place for me to be. I’m pissing on your living room carpet. I cannot help that. I’m a representative of the 80% of humanity that is stupid. I’m here to hold up our responsibility in this dialogue. My intention is to explain as clearly as effortlessly as within my means why stupid isn’t dumb.

    In that regard I finish with the following quick statements. …

    i) Not emotional intelligence
    ii) Not social intelligence

    80% of humanity isn’t primarily volatile, unpredictable, vague, irrational or subjective for the sake of emotion or socialization. That is way too high a price for far too little.

    iii) Heuristics

    Yes, heuristics sort of explains why most of humanity is irrational. Regrettably the concept of heuristics is confusing and misleading in an entrapping manner.

    I’ve said it (heuristics) and henceforth walk away from it …
    … Carrying on therefrom.

    • That’s too long and too detailed to respond point by point, so I will content myself with saying that overall i think you are right, in general terms. Most of these “diseases” are, I think, polar personality extremes that are distributed normally in ordinary populations. An educationalist once said to me that in a normal distribution, 5% of students are what used to be called “retarded” and therefore the same number are “gifted” (and both have problems in the ordinary population of students); it led me to thinking that this must be true also of all other personality traits. Those at the extremes will have troubles because the social expectations will be predicated upon the mode, and the further one deviates from that, the less social expectations will permit your behaviour and dispositions.

      And that is without even considering the question of the social construction of disease, which is a can of worms I would rather not dive into.

  7. Raving

    An Erratum before continuing ahead …
    (and also as a token of recognition to response)
    … with anticipation of continuing followup …

    which will happen when I am able to build up sufficient inertia of gumption.
    (… and am able to cut loose. Yes, it’s not pretty …)

    Raving: There are two intensive reasons. The 1st reason is far and away the greatest hurdle perversely.

    First Reason: … There are two sub-reasons

    a) These methodologies are extremely simple and very intense….

    b) [unstated] There is only the ‘objective’ viewpoint.

    It is difficult to say something worthwhile about irrational thought when the framework is to be ‘objective’ …, …, …, … or ‘objective’

    In a milieu where all substantive words are ‘object’ Wittgenstein and Whorfianism hold sway and rule the roost.

    The predicament is to say something tangible when the elements which are used to construct a ‘description’ are insubstantial.

    Second Reason: [reclassified]
    … Medicine concerns itself with pathology. We visit the physician to cure problems. …

  8. Re ASD and whether it’s a ridiculous class, my understanding is that the term was invented to provide a theory-neutral way of talking about autism, asperger’s syndrome, and the relationship between them.

    That is, some people say that asperger’s syndrome is a type of autism. Others say that asperger’s syndrome is completely distinct from autism. People in each camp refer to people in the other camp as idiots. So the term “autism spectrum disorder” was invented as a way of calling a truce: it provides a convenient way of talking about a group of disorders that resemble each other up to a point, without committing to any particular theoretical underpinning for those resemblances.

    In that capacity, I find it a useful term.

  9. Raving

    Finding 5 peculiar outliers and only shades in variation of those same peculiarities indicates just 5 items. The gradations don’t fill the voids in the sparse distribution.

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