Eating Disorders

Comorbidity in Eating Disorders: Real or Spurious?

A pragmatic approach to complex cases.

Posted Jun 16, 2020

Comorbidity is a complex topic, conceptually and clinically. The definition of comorbidity from a conceptual point of view refers to a situation in which "a distinct clinical entity appears during the course of a disease" — for example when a patient with diabetes develops Parkinson's disease. In this case, there are two distinct clinical entities and a lifetime concept is applied. 

The definition of comorbidity from a clinical point of view refers, instead, to a situation in which "two or more distinct clinical entities coexist." In this case, the prevalence of comorbidity depends on the definition of the disorders (i.e., the classification system and its diagnostic rules). 

In the field of mental health, where no specific biomarkers have been found so far, it is questionable whether two mental disorders are "distinct" clinical entities, or simply the result of the current classification of mental disorders which, based on symptom presented, encourages the application of multiple psychiatric diagnoses in the same patient.

Problems related to the definition of comorbidity can have important clinical consequences that affect the treatment. For example, the characteristics of depression are common in patients with eating disorders but may be evidence of either a co-existent clinical depression (‘true comorbidity’) or the direct consequence of underweight in anorexia nervosa or binge eating in bulimia nervosa (‘spurious comorbidity’) (see Figure 1). In the first case, clinical depression must be treated directly, while in the second case the treatment of the eating disorder should lead to a remission in the depressive features.

Riccardo Dalle Grave, MD
Figure 1. Features suggestive of secondary or co-existing clinical depression with the eating disorder
Source: Riccardo Dalle Grave, MD

Comorbidity in eating disorders

A narrative review of European studies concluded that more than 70% of people with eating disorders receive a diagnosis of psychiatric comorbidity. The most frequent co-existing mental disorders are anxiety disorders (>50%), mood disorders (>40%), self-harm (>20%), and substance use disorders (>10%).

It should be emphasized that data from the studies carried out present a wide variability in the rate of psychiatric comorbidity in eating disorders; for example, the prevalence of a lifetime history of an anxiety disorder has been reported in as few as 25% to as many as 75% of cases. This range inevitably casts significant doubts on the reliability of these observations. Likewise, studies that assessed the prevalence of personality disorders co-existing with eating disorders reported an even greater variability, ranging from 27% to 93%!

Methodological problems

Studies that have evaluated comorbidity in eating disorders suffer from serious methodological problems. For example, a distinction has not always been made whether the "comorbid" disorder occurred before or after the eating disorder; the samples evaluated often are small and/or includes diagnostic categories of eating disorders in different proportions; a large and heterogeneous number of diagnostic interviews and self-administered tests were used to assess comorbidity. However, the key problem is that most studies did not assess whether the characteristics of comorbidity were secondary to the low weight or disturbance in the diet

Comorbidity or complex cases?

The notion that there is only a subset of "complex cases" cannot be applied to eating disorders Indeed, almost all patients suffering from eating disorders can be considered complex cases. Most, as described above, meet the diagnostic criteria for one or more psychiatric disorders. Physical complications are common, and some patients have co-existing and interacting medical pathologies. Interpersonal difficulties are the norm, and the chronic course of the disorder can have a strongly negative impact on the development and interpersonal functioning of a person. All this shows that in patients with eating disorders, complexity is the rule rather than the exception.

The artificial division of complex clinical conditions into small pieces of psychiatric diagnosis may have the negative effects of preventing a more holistic approach to treatment and promoting an unjustified use of several drugs or interventions to treat single pieces of a broader and more complex clinical picture. Moreover, the inaccurate assessment and management of co-morbidities may have the paradoxical effect to defocus the treatment from key factors that maintain the eating disorder psychopathology and to deliver to the patients unnecessary and potentially harmful treatments.

A pragmatic approach to complex cases

In my clinical practice, I adopt a pragmatic approach to addressing psychiatric comorbidity associated with eating disorders. I recognize and eventually address comorbidity only when it is significant and has clinical implications. To this end, the manual of enhanced cognitive behavior therapy (CBT-E) for eating disorders divides comorbidities into three groups:

  1. Disorders that likely do not interfere with CBT-E, but probably respond to it. These disorders need to be recognized, monitored, and re-assessed during the treatment, but they are not given special attention. Examples are clinical depression secondary to the eating disorder and social anxiety attributable to the eating disorder.
  2. Disorders that likely interfere with CBT-E, but do not respond to it. These disorders need to be recognized, and a decision made about when to treat them (e.g., before or after, but not simultaneously with CBT-E). Examples are post-traumatic stress disorder, and obsessive-compulsive disorder (the possibility of associating CBT-E with an SSRI may be assessed, but not another psychological treatment).
  3. Disorders that interfere with CBT-E. These disorders need to be recognized and treated before starting CBT-E. Examples are continuous misuse of substances, acute psychosis, and clinical depression not secondary to the eating disorder.

References

Dalle Grave, & Calugi. (2020). Cognitive behavior therapy for adolescents with eating disorders. New York: Guilford Press.

Fairburn, Cooper, & Waller. (2008). Complex cases and comorbidity. In C. G. Fairburn (Ed.), Cognitive behavior therapy and eating disorders. New York: Guilford Press.