What is mental illness?

Illness is like the street you've driven down your whole life. So familiar you've never bothered to look around. We've all experienced illness, either first-hand or via someone we know, but rarely do we stop to wonder what it really is.

You might say it's when something mental or physical isn't working as it should be. But then who is to say how things should be working? This is easier to answer in relation to physical health, but still tricky. Pain, a loss of ability, a shortening of life expectancy, perhaps? These criteria seem far from satisfactory. Pain is highly subjective and can be triggered by mundane ailments like toothaches or stubbed toes - are they really illnesses? Loss of ability seems more objective, but is surely only a necessary rather than sufficient criterion. After all, temporary fatigue and age both cause a loss of ability. Similarly, driving cars fast and other dangerous hobbies will likely shorten your life. These philosophical conundrums are magnified when it comes to mental illness. When does a hobbyist collector become a compulsive hoarder? How tightly do the shackles of shyness have to constrain a person before he or she is considered ill? What if the solitude of the social phobic allows them to pen great poetry or novels - is that adaptive or maladaptive?

The psychiatrist Dan Stein at the University of Cape Town and five others have tackled these issues and more in an editorial for the journal Psychological Medicine. Their approach has been to consider the definition of mental disorder stated in the fourth edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM), and to recommend modifications to it to be used in the forthcoming fifth edition, for which they are Work Group members.

Stein's team propose that a mental disorder has five features. First, it is a behavioural or psychological syndrome or pattern that occurs in the individual. This emphasis on the individual rules out dysfunctions that exist at the relationship or group level. Interestingly, they acknowledge that this causes problems for the DSM IV diagnosis of Shared Psychotic Disorder (or Folie à deux) in which delusions are passed from one person to another.

Second, the symptoms of a mental disorder are clinically significant distress (e.g. a painful symptom) or disability (i.e. impairment in one more important areas of functioning). Here they explain that 'clinically significant' is meant to distinguish from 'milder distress or difficulty in functioning that may not warrant clinical attention'. They acknowledge that clinical significance is tricky to 'operationalise', but argue that it 'remains useful in differentiating disorder from normality'. Readers will notice that this point doesn't really help us distinguish between personality traits like shyness and disorders like social phobia - it merely acknowledges that somewhere a line of severity is crossed.

Third, the behaviour or symptoms must not merely be an expectable response to common stressors and losses (e.g. the loss of a loved one) or a culturally sanctioned response to a particular event (e.g. trance states in religious rituals). Similar to the last, this point is also intended to help prevent the medicalisation of psychological reactions that are an expected part of life. However, Stein's team acknowledge this is murky territory - for example, they point to the contentious boundaries between 'normal and pathological bereavement.' Also, so-called 'normal' reactions to distress are often associated with increased risk of more serious problems later on - in other words, from a clinical point of view they shouldn't be ignored.

Fourth, a mental disorder must reflect an underlying psychobiological dysfunction. This is an acknowledgement that all illnesses of the mind have an underlying neural correlate. Meanwhile, the 'dysfunction' described here can be interpreted either in evolutionary terms whereby some faculty is not working as it evolved to, or in terms of statistical deviance from what's normal according to the client's own background and future goals. Neither is without problems. Evolutionary interpretations tend to be speculative, and what counts as dysfunctional is subjective and influenced by context. Stein's team give the example of living in a dangerous urban area 'where it may be adaptive to join a gang, but where this requires participating in behaviours listed in the diagnostic criteria for conduct disorder.'

Fifth, to be a mental disorder, Stein and his colleagues say a person's behaviour or symptoms should not primarily be a result of social deviance or conflicts with society. This is yet another safeguard against over-pathologising behaviour. The criterion is required, Stein's team say, 'because psychiatric diagnoses have been used for political purposes in the past and potential future misuse cannot be ruled out'. Indeed, one need only consider the fact that homosexuality was included in the DSM until as recently as 1973 to see the inappropriate influence of social mores on psychiatry.

Finally, Stein and his co-authors outline several further points for DSM 5 to bear in mind when considering what constitutes a mental disorder, including: that the potential benefits of adding a condition to the new DSM should outweigh the potential harms, and that any new diagnostic category should be clinically useful - that is: 'facilitate the process of patient evaluation and treatment rather than hinder it.'

As you can see from these highlights, there are many grey areas when it comes to defining what constitutes a mental illness, especially in relation to judging what counts as abnormal distress or dysfunction. As the authors conclude, the basic position (acknowledged in DSM IV) that mental disorder cannot be 'precisely operationally defined seems ... to be basically correct.' However, on a more optimistic note, Stein's team further argue that the classification system can improve over time as the scientific knowledge base progresses. 'Disorders are more than mere "labels",' they conclude, 'and progress towards a more scientifically valid and more clinically useful nomenclature is possible.'

What do you think? Do you share their optimism?
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Stein, D., Phillips, K., Bolton, D., Fulford, K., Sadler, J., and Kendler, K. (2010). What is a mental/psychiatric disorder? From DSM-IV to DSM-V. Psychological Medicine, 40 (11), 1759-1765 DOI: 10.1017/S0033291709992261

Further reading on the Digest blog:
Are mental disorders real?
New data suggests one in two of us experience mental illness in our life-times.
Psychotherapy has drug-like effect on the brain.

This post is an invited contribution to a mini blogging carnival on the topic 'What is psychopathology?' hosted by The Thoughtful Animal blog.