Eating Disorders

People may come to be more similar when they are stuck within a morbid process than when they are well because the range of their behaviour and experience is at least in part constrained by processes in which such biological mechanisms are playing some limiting part. Tolstoy wrote, 'all happy families resemble one another, but each unhappy family is unhappy in its own way'. This is questionable even with regard to families and unhappiness, but with individuals and disorder it seems likely that the reverse is true. The range of what is morbid is narrower than the range of the non-morbid. Antipsychiatrists tend to emphasise the prescriptive nature of 'normality' and to portray the person who is 'labelled' mentally disordered as something of a free spirit. However, the psychiatric perspective is different.

The patient suffering from a mental disorder is seen as constrained and trapped by forces that are outwith his or her control. It is the sufferer who is the tram compared with the normal person who resembles the bus in having much more freedom. Both the bus and the tram are limited by their physical attributes but the tram is additionally constrained by the rails. Study of the patterns of disorder could give clues as to the nature of these 'rails'.

So what is the status of our current attempts at classification? What patterns can we discern in people with eating disorders? How well do our conventional diagnoses map these patterns? And do any of these patterns suggest the presence of plausible mechanisms of aetiological significance? Do our categories promise to be more than convenient pigeonholes? Are there 'real' disorders out there?

What follows is a clinician's view of our present classifications and some speculation about what mechanisms and natural kinds might lurk beneath the surface of their syndromes and diagnostic criteria.

An ideal classification should consist of categories that are mutually exclusive and collectively exhaustive. Its entities should be discreet and together they should cover the ground. The classification of eating disorders measures up to these standards rather poorly. The canon contains only two major categories - anorexia nervosa (AN) and bulimia nervosa (BN). Anorexia nervosa has low weight as an essential criterion. Bulimia nervosa has binge eating as a necessary criterion. The two disorders share the criterion of what in broad terms might be described as an over-concern about body weight and size although some would see a major difference in degree or emphasis in the typical ideas held by sufferers from AN and BN. In DSM-IV, AN takes precedence over BN in the sense that the presence of the former bars the diagnosis of the latter. In contrast in the earlier version, DSM-III-R, it was possible to make the dual diagnosis of both AN and Bulimia Nervosa.

There is in DSM-IV, however, a new subclassification of AN into binge - purging and pure restricting subtypes. The rules in both of these sets of criteria represent different responses to the fact that low weight and bingeing occur together commonly and that, hence, the cardinal features of AN and BN are closely related even in cross-section. When longitudinal course over time is considered then the overlap becomes even more striking. In many series, a substantial minority of BN sufferers have a past history of AN. The reverse transition from BN to AN is less common, but does occur. Thus, AN and BN are far from being entirely discreet disorders and can be made to seem so only by dint of a certain sophistry. However, if the classification of the eating disorders fails to meet fully the ideal of providing discreet entities, it fails even more in respect of the second criterion, that of covering the ground. Many people present with eating disorders that fulfil criteria for neither of the two main disorders.

The classification of the eating disorders achieves the standard of being collectively exhaustive only through having the `rag bag' or residual category of EDNOS. The EDNOS category has only one positive criterion and one negative criterion. The positive criterion is that the individual being thus diagnosed should be deemed to have an eating disorder of clinical severity-a disorder that matters. The negative criterion is that the disorder should not fulfil criteria for AN or BN.

The EDNOS category thus defined is common. In many clinical series of people presenting to eating disorders services it is the single most common diagnosis and in some forms the majority of cases. Furthermore, as with AN and BN, the longitudinal perspective is illuminating but complicating. Many cases of the two main disorders change their characteristics over time so that those who have suffered from either at one time come later to suffer from neither but continue to have a clinically significant eating disorder. They can then be diagnosed only as being in a state of EDNOS. It is less clear whether people commonly move from a time of sustained EDNOS into one of the classic disorders.