The Diagnostic Statistical Manual of Mental Disorders, Fifth Edition [DSM 5] defines eating disorders within four categories: Anorexia Nervosa [AN], Bulimia Nervosa [BN], Binge Eating Disorder [BED] and Eating Disorder Not Otherwise Specified [EDNOS]. The DSM 5 contains universal, categorical diagnostic criteria and possible treatments for mental health disorders such as the eating disorders listed above. This assists clinicians in identifying disorders through the classification of symptoms. However, patients often do not meet the strict criteria within the DSM 5 and this has a large impact on the diagnosis and treatment of these disorders. This essay will discuss the implications for diagnosis and treatment of eating disorders, such as diagnostic cross over and the unclear areas of the DSM that still exist in the most current model, along with the significance of categorical versus dimensional perspectives on the diagnosis of mental illness.
Each category within the DSM 5 contains specific diagnostic criteria aimed at providing clinical psychologists with the tools necessary to diagnose, and therefore potentially treat an eating disorder. These diagnostic criteria are extremely restrictive, including set time frames of behaviour. For example, the diagnostic criteria for Bulimia Nervosa includes recurrent episodes of binge eating, “in a discrete period of time [within any 2 hour period], an amount of food that is definitely larger than most people would eat during a similar period of time… “ Due to the narrow nature of diagnostic criteria for eating disorders, any uncertainty or fluctuation of a patient symptoms often results in a shift of diagnosis. The consequences of this are extremely detrimental, both to the psychological well being of the patient and family, as well as previous treatment and the modification of treatment that would follow.
The instability of diagnosis of the four eating disorder categories is a result of the shared psychopathology that characterizes each disorder, the close relationship of the diagnoses reiterated by the phenomenon of diagnostic crossover over time [Milos et al. 2005] and the awareness of clinical psychologists that the instability of diagnoses is common, therefore possibly providing a clinician with less pressure to correctly diagnose the disorder initially.
This is highlighted in a study conducted by Milos et al.  on 277 women aged 17-50 with an eating disorder of clinical severity. Four psychologists involved in the study diagnosed the eating disorders with the DSM 4. An assessment at 12 months and then again at 30 months showed of the 277 participants, 53% crossed over from one eating disorder to another and the diagnostic migration was evident in all three diagnostic groups. The main finding from this study was that the diagnostic stability of eating disorders is low, with only a third of patients retaining their original diagnosis over a 30-month period. Although the DSM 4 was used and therefore the fourth category of binge eating was not included, a similar and more recent study that included this newest category again concluded that at a 2 year follow up, overall 28.9% of the patients maintained their admission diagnosis [Fichter & Quadflieg 2007]. The considerable fluctuation between the four diagnoses is startling and can have a number of significant effects to the patient and their treatment.
The implications of such instability in diagnosis between each eating disorder emphasizes the continuing limitations that can still be identified in the most recent diagnostic criteria of the DSM 5 [Milos et al. 2005]. This can be seen if an individual’s weight or eating