What are the key considerations in the differential diagnosis of bulimia?

Differential Diagnosis of Bulimia Nervosa

When evaluating a patient with suspected bulimia nervosa, the key differential considerations include other eating disorders (particularly anorexia nervosa with binge-purge subtype), gastrointestinal disorders causing vomiting, psychiatric conditions with disordered eating, and rumination syndrome.

Primary Psychiatric Differentials

Anorexia Nervosa

• Anorexia nervosa is distinguished by significantly low body weight (<75% ideal body weight or BMI <16 kg/m²), intense fear of weight gain, and body image distortion 1, 2
• The DSM-5 criteria require: (1) persistent restriction of energy intake leading to significantly low body weight; (2) intense fear of gaining weight or persistent behavior interfering with weight gain; (3) disturbance in body weight/shape perception 1
• Unlike bulimia, patients with anorexia nervosa typically maintain low body weight, whereas bulimia patients are often normal or above normal weight 3
• Both conditions can involve purging behaviors, but the presence of significantly low body weight points toward anorexia nervosa 1

Avoidant/Restrictive Food Intake Disorder (ARFID)

• Patients with ARFID have disordered eating patterns due to psychosocial problems but lack the body image distortion and fear of weight gain characteristic of bulimia 1
• These patients may have disordered gut motility partly due to undernutrition and past drug treatments 1

Gastrointestinal Differentials

Gastroparesis

• Vomiting must be differentiated from regurgitation, rumination, and bulimia through careful history of duration, frequency, severity, and associated symptoms 1
• Gastroparesis presents with nausea, vomiting, and postprandial abdominal fullness, similar to bulimia 1
• Key distinguishing features: gastroparesis symptoms are not intentionally induced and lack the binge-eating component 1
• Gastric emptying scintigraphy can objectively demonstrate delayed gastric emptying in gastroparesis (test duration must be at least 2 hours, preferably 4 hours) 1

Rumination Syndrome

• Rumination involves effortless regurgitation of recently ingested food without nausea, which is then re-chewed and re-swallowed 1
• Antroduodenal manometry can help diagnose rumination syndrome and differentiate it from gastroparesis and bulimia 1
• Unlike bulimia, rumination lacks the psychological components of body image distortion and compensatory behavior intent 1

Other GI Disorders

• Inflammatory bowel disease, acid peptic diseases, and intestinal motility disorders (such as achalasia) may mimic eating disorders 4
• These can usually be distinguished by applying DSM diagnostic criteria for eating disorders and obtaining biochemical tests 4
• Hyperamylasemia of salivary origin is regularly seen in bulimia but may lead to erroneous diagnosis of pancreatitis 4

Functional Gastrointestinal Disorders

Functional Dyspepsia and Irritable Bowel Syndrome

• Many symptoms of small intestinal dysmotility overlap with functional gastrointestinal disorders (IBS, functional dyspepsia, cyclical vomiting, functional bloating) 1
• The critical distinguishing feature is that significant malnutrition is rarely a consequence of functional disorders, whereas it commonly occurs in eating disorders 1
• Functional disorders may have genetic and psychosocial influences similar to eating disorders but lack the intentional compensatory behaviors 1

Key Diagnostic Features to Establish Bulimia

Clinical Assessment

• Parotid gland enlargement (appearing as swollen cheeks or jawline) is pathognomonic for bulimia nervosa and results from repeated self-induced vomiting 5
• Russell's sign (calluses or scarring on the dorsum of the hand from inducing vomiting) is a specific physical finding 5, 6
• Dental enamel erosion and poor gum health from repeated acid exposure distinguish bulimia from functional disorders 5, 6
• Document the types and frequency of purging behaviors (vomiting, laxative use, diuretic use, excessive exercise) 7

Laboratory Findings

• Hypokalemia and hypochloremic metabolic alkalosis strongly suggest purging behaviors 1, 7, 6
• Elevated serum amylase (of salivary origin) is common in active bulimia 6, 4
• Obtain ECG to assess for QTc prolongation, which indicates risk of sudden cardiac death 7, 2
• Complete blood count and comprehensive metabolic panel help identify electrolyte abnormalities 7

Behavioral Criteria

• Bulimia is defined by recurrent binge eating episodes followed by inappropriate compensatory behaviors (vomiting, fasting, excessive exercise, laxative/diuretic misuse) 8, 3
• Binge eating typically begins in late adolescence after a period of dieting, with self-induced vomiting following about a year later 9
• The disorder affects 5-20% of college-age women and is 10 times more common in females than males 3, 9

Common Pitfalls to Avoid

• Do not assume normal laboratory results exclude serious illness—more than half of adolescents with eating disorders have normal test results despite being medically unstable 7
• Do not delay ECG while waiting for other test results, as cardiac complications are the leading cause of death in eating disorders 7
• Avoid escalating to invasive nutrition support in patients with functional symptoms in the absence of objective biochemical disturbances or those with high/normal BMI 1
• Screen for comorbid psychiatric conditions (depression, anxiety, OCD, substance abuse, suicidality) as these frequently coexist with bulimia and may complicate diagnosis 7, 3