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genetics

The End of Kraepelin’s Dichotomy

23 Jan, 09 | by Steven Reid, Evidence-Based Mental Health

No, don’t worry; this isn’t a blog about metaphysics. It was over 100 years ago that Emil Kraepelin, widely considered the father of contemporary psychiatry, divided psychosis into two discrete disorders: dementia praecox (schizophrenia) and manic-depressive insanity (bipolar disorder). Hence the dichotomy, which remains a hallmark of the classification of mental illness.

 

This categorical approach to diagnosis has plenty of critics but the divide remains firmly in place. Why? Partly because making a psychiatric diagnosis is often an uncertain business. It’s inherently appealing to have just two options to choose from when trying to make sense of a complex clinical picture. Plus the textbooks tell you it’s straightforward: schizophrenia means an enduring illness, with a flat, unreactive mood, and inevitably a poor outcome, in contrast to bipolar illness which is episodic with dramatic changes in mood, and of course that flair for creativity. Well life’s not actually like that. In clinical practice it’s often difficult to discriminate between the two. Take a look at the casenotes of a person with schizophrenia and at some point it’s likely someone will have made a diagnosis of bipolar disorder, and vice versa. In fact we’ve even had to invent a new diagnosis – schizoaffective disorder – for those cases when you just can’t make up your mind. So there has been disquiet about Kraepelin’s dichotomy for some time and now we have a behemoth of a study which may well prove to be the final nail in its coffin.

 

Published in the Lancet this is a population-based study including over nine million Swedes, that teases apart the genetic and environmental contributions to both schizophrenia and bipolar disorder. Previous genetic studies have been nowhere near as big so the findings are compelling. We know that genes are important in both schizophrenia and bipolar disorder but here it’s demonstrated that they share a common genetic cause. First-degree relatives of people with bipolar illness had an increased risk for schizophrenia, including adopted children to biological parents with bipolar disorder. Similarly, relatives of those with schizophrenia were at increased risk of bipolar disorder.

 

So what next? Out with the old diagnostic criteria? Perhaps…it certainly gives the committees debating the next version of the psychiatrists’ diagnostic manual (DSM-V) plenty to think about. Maybe it’s time we moved toward a psychosis-spectrum disorder with a renewed emphasis on symptoms. After all, it’s the symptoms that predict response to a specific treatment, not the diagnosis. And what of Kraepelin, would he approve? Well he was having doubts about his own dichotomy back in 1920, “No experienced psychiatrist will deny that there is an alarmingly large number of cases in which it seems impossible, in spite of the most careful observation, to make a firm diagnosis…. It is becoming increasingly clear that we cannot distinguish satisfactorily between these two illnesses and this brings home the suspicion that our formulation of the problem may be incorrect”.

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