Difficult Diagnosis: AN or BN

Is this anorexia nervosa (with binging) or bulimia nervosa?

When binge/purge episodes are present, it can be difficult to distinguish between anorexia nervosa (binge/purge subtype) and bulimia nervosa. 

The key difference between these diagnoses is weight:

A diagnosis of anorexia nervosa necessitates severe low weight, that is less than minimally normal. 

In contrast, people with bulimia nervosa tend to fall within, or above, their most healthy weight range. 

In addition, people with anorexia nervosa (binge/purge subtype) typically report binges that are subjective in size, rather than the objective binges observed in bulimia nervosa. 

Note: If significant weight loss is present but BMI is not in underweight range, it may be worth exploring a diagnosis of atypical anorexia nervosa. 

About Anorexia Nervosa

AN is characterised by: 

• Extreme food restriction 
• Significant weight loss and/or significantly low weight that is less than minimally normal 
• Intense fear of gaining weight1.

Presentations can be divided into two subtypes, with high rates of crossover between the two.  

• Restrictive subtype:
• Achieves weight loss primarily through restriction of caloric intake and/or excessive exercise 
• Binge/purge subtype:
• Involves episodes of binge eating and compensatory behaviours (i.e., self-induced vomiting, laxative misuse)1.

These behaviours result in malnutrition and starvation, which can lead to a range of physical and psychological health complications and, in some cases, death.  

About Bulimia Nervosa 

BN is characterised by: 

• Recurrent episodes of binge eating 
• Unhealthy compensatory behaviour aimed at preventing weight gain (i.e. excessive exercise, self-induced purging, laxative abuse) 

Bulimia nervosa is often used as a way of dealing with underlying personal, emotional and psychological difficulties. 

It can be experienced by the individual as helping them to function by numbing their emotions, providing a distraction or a sense of accomplishment, and thereby helping them feel in control.