A tool for action

Many psychologists as well as psychiatrists see some merits in the diagnostic approach. About a third of the people involved in the taskforce drawing up DSM-5 were psychologists. For many, their decision to accept a diagnostic approach is purely practical - they see DSM as a tool for categorising problems and suggesting what might help. In the next chapter, we will examine some of the evidence concerning the extent to which diagnoses are useful in assisting treatment decisions. In short, I believe diagnoses are unhelpful.

As we shall see in the next chapter, it is very difficult to predict what treatments people will find helpful on the basis of the diagnosis they receive. In physical medicine, specific types of drugs are helpful for specific problems. For example, penicillin is a specific treatment for bacterial infection and not for viral infection. It is different with psychiatric medication. Although you might imagine that the drugs known as 'antipsychotics' are specific treatments for 'schizophrenia', this is not the case. Not all people with a diagnosis of 'schizophrenia' benefit significantly. At the same time, some people with other diagnoses do seem to benefit from these drugs. If you are experiencing a manic episode, for example, you may find that 'antipsychotic' medication offers some temporary respite. This is not what you would expect if 'bipolar disorder' were 'carved at the joints' from 'schizophrenia'. Proponents of diagnoses usually stress that diagnosis is needed to decide the right treatment. But in reality psychiatric diagnosis appears almost irrelevant in this regard and some psychiatrists, notably Dr Joanna Moncrieff, suggest that diagnosis should not be used as a basis for prescribing. This seems a rather fatal problem for the diagnostic approach.

Diagnoses also appear to have little practical utility when it comes to prognosis. A valid diagnosis, a diagnosis that means something in the real world, should say something about the outcome that people given the diagnosis should expect. Again, however (with the exception of neurological diseases and learning disability, which are rather different) the outcomes for people given nearly every diagnosis are highly variable. Moreover, each person's outcome appears dependent much more on their social situation than on their diagnosis - so whether they are in a relationship, whether they have friends, whether they have a job, whether they have somewhere decent to live. Health care professionals, quite correctly, tell people that there are a huge range of possible outcomes, and (again correctly) that many things can be done to affect their prognosis. Arguably this all makes diagnosis rather redundant.

There is a perception that people with psychiatric diagnoses are more likely than others to be violent. However, in fact, very few acts of violence are committed by people with a history of mental health problems. The most important factors predicting violence are: having a history of violence, being male and using alcohol. Specific diagnoses like 'schizophrenia' do not predict dangerousness. Some specific experiences and beliefs, such as a conviction that others intend to do you physical harm, or hearing voices telling you to do something violent, are associated with a small increased risk. But even among people who have these experiences, few actually end up acting on them. Even where people do, the association is with the specific experiences or beliefs rather than with a particular diagnosis. Despite this story of failure, many of my colleagues who advocate the use of diagnosis in mental health care appear still to rely on the myth of utility - the idea that diagnoses are useful. One (medically-qualified) contributor to an on-line blog (hosted by the well-respected Oxford University Press) tried to defuse this row by saying that: 'clinicians need to communicate to each other, and even a wrong diagnosis allows them to do so.' This is not only foolish, it's dangerous. It suggests not only that clinicians can permit their care to be guided by 'wrong' diagnoses, but they should (perhaps need to) share their errors with colleagues. Another contributor suggested that we need to regard diagnoses such as schizophrenia as 'heterogeneous diagnoses'. So we have one influential proponent suggesting that diagnoses are useful even if they are 'wrong', and another suggesting that they can be catch-all or 'heterogeneous'. Whilst it seems very strange to suggest that something that is wrong can also be necessary, it is truer to say that psychiatric diagnoses are 'heterogeneous'; research suggests that they simply do not represent discrete phenomena.

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