Overvalued ideas or delusions in anorexia nervosa?

Anorexia nervosa (AN) is a psychiatric illness characterised by a disturbance in the experience of one’s own body weight or shape, leading to significantly low body weight. These distorted beliefs relating to body image are so severe that the resulting starvation leads to death in a significant proportion of patients. Despite these disturbed ideas or beliefs causing significant morbidity and mortality in AN, their mechanisms remain unclear.

Unusual beliefs in mental illness are typically categorised using three classifications: obsessions, delusions and overvalued ideas. Obsessions are defined as intrusive and persistent ideas, thoughts, impulses or images, which cause marked anxiety or distress, whereas delusions describe false beliefs based on incorrect inferences and are firmly sustained despite the opinion of others or evidence to the contrary. In contrast, an overvalued idea is defined as an unreasonable and sustained belief that is not obsessional in nature and is not maintained with delusional intensity (i.e. the individual can acknowledge that the belief might not be true). Although the categorisation of unusual beliefs based on the level of insight is controversial given that it does not take into consideration dimensions other than the strength and abnormality of the belief, such as the level of distress and affect, and the ego-syntonic nature of the belief, it is the most common dimension used to differentiate unusual beliefs in mental illness. Typically in AN, beliefs of body image distortion are described as overvalued ideas, implying that their nature is neither obsessional nor delusional. However, the justification for these beliefs as overvalued ideas lacks significant research evidence.

The Brown Assessment of Beliefs Scale (BABS) has been the most widely used measure to examine unusual beliefs in psychopathology, particularly in AN. It rates a number of dimensions that underlie unusual beliefs, namely, overvalued ideas/delusions of reference, conviction, perception of others’ views of beliefs, explanation of differing views, fixity of ideas, attempt to disprove beliefs and insight (Eisen et al., 1998). The BABS is based on the notion that insight, or degree of delusionality, exists on a continuum ranging from good insight (obsessions) to poor insight (overvalued ideas) to no insight (delusions). Using this measure, studies have reported varying findings in relation to the type of unusual beliefs held by individuals with AN.

Hartmann et al. (2013) investigated delusionality of the primary body image concern in groups of AN and body dysmorphic disorder (BDD) patients. Although BDD patients were found to score higher on the BABS than AN patients, 16% of the AN group were reported to score within the delusional belief range and 26% within the overvalued ideas range. The degree of delusionality was also not associated with measures of body image or with clinical measures, such as body mass index (BMI) and illness duration, in either group. However, delusionality was associated with body shape concern as measured by the Eating Disorder Examination (EDE) and the drive for thinness variable of the Eating Disorder Inventory (EDI). Similarly, Steinglass et al. (2007) reported that 20% of their AN sample met criteria for delusional beliefs, with a further 28% showing poor insight. BABS scores were also correlated with drive for thinness, but not with BMI or illness duration, similar to the study by Hartmann et al. (2013). A more recent study by McKenna et al. (2014) reported similar findings, with 25.9% of AN patients lacking insight and 29.6% demonstrating poor insight into their dominant eating disorder–related belief.

Given the significance of delusional beliefs in conditions such as schizophrenia, Mountjoy et al. (2014) compared BABS scores in AN relative to this group. The findings of the study indicated a lower rate of delusional beliefs and overvalued ideas in the AN group (10% and 30%, respectively) compared to the schizophrenia group (37% and 45%, respectively). Delusion intensity as rated by the Psychotic Symptom Rating Scale, however, was found to be higher in the AN group than in the schizophrenia group. Furthermore, both AN and schizophrenia patients endorsed a greater number of delusional beliefs than healthy individuals on the Peters Delusion Inventory, with scores on distress and preoccupation being the highest in AN.

Overall, the studies undertaken, to date, specifically investigating unusual beliefs in AN report not only high rates of overvalued ideas (ranging from 26% to 30%) but also very high rates of beliefs that can be classified as delusions (ranging from 10% to 45.5%). The notion that unusual beliefs in AN are most likely to represent overvalued ideas with poor insight is not justified by this literature. Instead, delusions with no insight appear to be almost as present as overvalued ideas in AN samples. However, it is important to note that a significant proportion of AN patients in these samples did not report delusional beliefs or overvalued ideas, but instead showed good insight. Together, these results suggest that unusual beliefs in AN do not fall neatly into one category but occur along a spectrum ranging from very good insight to no insight. Examples along the spectrum include beliefs such as ‘when I pass people in the street, they are looking at me and are disgusted by how fat I am’ (delusion), and ‘to be loved, I must be thin’ (overvalued idea). Indeed, such a continuum idea has been described across a number of psychopathologies, including schizophrenia, BDD, and obsessive-compulsive disorder (OCD).

In conclusion, we argue that although data are limited, one can no longer ignore the proposition that distorted body image beliefs in AN lie on a continuum from good insight to delusional. Such a specifier is now present when one is assessing body image beliefs in BDD when using Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM 5) criteria. We propose a similar specifier needs to be adopted in AN. This will allow the distinction of unusual beliefs in AN patients, enabling more personalised treatment.