31st January 2024

Differential diagnoses

There are two types of differential diagnoses to be considered, but in all cases less common than anorexia or bulimia. 

Psychiatric differentials

Firstly, there are other psychiatric disorders that can present physical health impacts from reduced eating, but the psychological factors driving disordered eating are different. These would include:

• Depressive disorders, where motivation and anhedonia lead to self-neglect and reduced eating. This often requires quite a severe depressive episode and delayed presentation to impact on physical health.
• Obsessive-compulsive disorder, where obsessive thoughts and corresponding compulsion lead to reduced intake, e.g., needing to complete a ritual means there is no time to eat in the person’s schedule.
• Psychotic disorders (e.g., schizophrenia), where delusions or gustatory (taste) hallucinations mean a person believes food is poisoned or inedible items are food. Rarely a person might have a delusional belief of being overweight as part of their psychotic disorder. This is not usually the presenting symptom. 
• Attention Deficit Hyperactivity Disorder, either due to appetite reduction secondary to amphetamines, or where hyperactivity and distractibility lead to unintentional excessive exercise and inability to finish a meal.
• Personality disorders, where food refusal, excessive exercise or purging is a form of self-harm

Physical health differentials

Organic disorders leading to weight loss tend to be less common than the disorders above, and it is important not to fall into the trap of ordering a series of investigations for organic disorders whilst there is a person rapidly losing weight. The key point to determine the difference between an eating disorder and their differentials is the history of food avoidance. The only exception might be those who struggle to communicate and may be refusing food due to pain on swallowing or indigestion. Key organic differentials would include:

• Malabsorption disorders: Coeliac disease or inflammatory bowel disease. If comorbid coeliac is suspected, then it may be falsely negative in someone with low gluten intake. A CRP can be useful to add to blood tests to investigate inflammatory bowel disease. 
• Malignancy. Especially those causing brain-occupying lesions that might also induce vomiting 
• Chronic infections, e.g. HIV, tuberculosis
• Endocrine disorders, which may also cause a secondary amenorrhea
• Diabetes, though there is a high comorbidity between type 1 diabetes and anorexia

References

• National Institute for Health and Care Excellence (2017). Eating disorders: recognition and treatment. (NICE Guideline number 69). https://www.nice.org.uk/guidance/ng69
• Royal College of Psychiatrists (2022). MEED. Medical Emergencies in Eating Disorders. RCPsych Guideline CR 233
• Semple, D. & Smyth, R (ed). Oxford Handbook of Psychiatry 2nd Edition.(2009) Oxford University Press