Anorexia Nervosa and Bulimia Nervosa are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.
Anorexia Nervosa vs Bulimia Nervosa at a glance
Anorexia Nervosa: Restriction of intake leading to significantly low body weight, intense fear of weight gain, and disturbed body image.
Bulimia Nervosa: Recurrent binge eating with inappropriate compensatory behaviors; normal or above-normal weight.
Try two board-style questions on Anorexia Nervosa vs Bulimia Nervosa
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Question 1PsychiatryEasy
A 16-year-old girl is brought in by her parents for concern about her eating habits. She has lost 18 lbs over 3 months and weighs 88 lbs (BMI 15.8). She exercises 2 hours daily and believes she is fat. She has had amenorrhea for 4 months. HR is 48, and labs show hypokalemia and prolonged QTc. Which of the following is the most likely cause of mortality in this condition?
AAspiration pneumonia
BHepatic failure
CSuicide
DCardiac arrhythmia
Reveal answer & full explanation
Correct answer: D — Cardiac arrhythmia
AAspiration pneumonia
BHepatic failure
CSuicide
DCardiac arrhythmia✓
Why Cardiac arrhythmia is correct
This is anorexia nervosa with medical instability: bradycardia (HR 48), hypokalemia, and prolonged QTc
Cardiac arrhythmia from electrolyte disturbance and QTc prolongation is the leading cause of death in anorexia nervosa
Medical instability warrants hospitalization
Aspiration pneumonia can complicate purging or refeeding but is not a leading cause of death in anorexia nervosa
Hepatic failure is rare in anorexia nervosa; starvation more often produces only mild transaminase elevation
Additional high-yield points
Refeeding syndrome (hypophosphatemia) is a major risk during initial nutritional rehabilitation
Suicide is the second leading cause of death in anorexia nervosa
Question 2PsychiatryEasy
A 19-year-old woman presents with recurrent episodes of uncontrollable eating of large amounts of food followed by self-induced vomiting. She feels intense shame after these episodes. BMI is 21. Exam reveals parotid gland enlargement and dental enamel erosion. Which lab abnormality is most commonly found?
AHyperchloremic non-anion gap metabolic acidosis
BElevated BUN and creatinine
CHypokalemic hypochloremic metabolic alkalosis
DHyponatremia
Reveal answer & full explanation
Correct answer: C — Hypokalemic hypochloremic metabolic alkalosis
AHyperchloremic non-anion gap metabolic acidosis
BElevated BUN and creatinine
CHypokalemic hypochloremic metabolic alkalosis✓
DHyponatremia
Why Hypokalemic hypochloremic metabolic alkalosis is correct
This is bulimia nervosa: binge-purge cycle with normal weight (BMI 21), which distinguishes it from anorexia.
Repeated vomiting causes loss of HCl, leading to metabolic alkalosis, hypokalemia (K+ lost in vomit and renal wasting from aldosterone activation), and hypochloremia.
Parotid hypertrophy and dental erosions are classic exam findings; Russell's sign (calluses on knuckles) is another classic finding.
Why the others are wrong
Hyperchloremic non-anion gap metabolic acidosis — the acid-base pattern of laxative-predominant purging, in which bicarbonate is lost in stool; this patient purges by self-induced vomiting, which produces the opposite picture.
Elevated BUN and creatinine — BUN/Cr elevation may be seen with dehydration, but hypokalemia is the most specific electrolyte finding in bulimia nervosa.
Hyponatremia — not the characteristic electrolyte disturbance of purging behavior.
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Restriction of intake leading to significantly low body weight, intense fear of weight gain, and disturbed body image.
Recurrent binge eating with inappropriate compensatory behaviors; normal or above-normal weight.
Classic presentation
Severe dietary restriction; rule-driven eating; excessive exercise; calorie counting; body checking; Subtypes: restricting type vs binge-eating/purging type; Amenorrhea common but not required for DSM-5-TR diagnosis; Cold intolerance, fatigue, constipation, dizziness, syncope; Cachexia, lanugo, dry skin, brittle hair, peripheral edema;…
Binge: eating an objectively large amount of food in <2 hours with sense of loss of control; Compensatory behaviors: self-induced vomiting (most common), laxative or diuretic misuse, fasting, excessive exercise; Both occur on average >=1/week for >=3 months; Body shape and weight unduly influence self-evaluation; Russell's sign (knuckle…
Workup / key labs
DSM-5-TR: (A) Restriction of energy intake relative to requirements leading to significantly low body weight in context of age/sex/developmental trajectory/health; (B) Intense fear of gaining weight or becoming fat, or persistent behavior interfering with weight gain; (C) Disturbance in body weight/shape experience, undue influence on…
DSM-5-TR: (A) Recurrent binge eating — large amount + loss of control; (B) Recurrent inappropriate compensatory behaviors; (C) Both occur on average >=1/week for >=3 months; (D) Self-evaluation unduly influenced by body shape/weight; (E) Disturbance does not occur exclusively during anorexia nervosa episodes. Severity by frequency: mild…
Imaging
DEXA for bone density; ECG essential prior to refeeding
Not routinely indicated; CXR if subcutaneous emphysema or chest pain (Boerhaave)
First-line treatment
Multidisciplinary team — primary care, mental health, dietitian, family; Family-based treatment (Maudsley) — first-line for adolescents; Cognitive behavioral therapy for eating disorders (CBT-ED), enhanced CBT (CBT-E) — adults; Nutritional rehabilitation with structured meal plan and gradual weight restoration; Medical hospitalization…
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