A 20-year-old college student comes to the office due to fatigue and decreased exercise tolerance. She says, "I used to run 5 miles every day, but for the past month I get out of breath after running 3 miles. I need to keep running so I don't get any fatter than I already am." The patient also reports difficulty concentrating in class, depressed mood, constipation, and abdominal bloating. Her appetite is normal, but she admits to occasionally forcing herself to vomit to prevent weight gain. Physical examination is significant for dry skin, painless bilateral parotid swelling, pharyngeal erythema, and hypoactive bowel sounds. Temperature is 36.2 C (97.2 F), blood pressure is 100/60 mm Hg, pulse is 62/min, and respirations are 16/min. BMI is 17.5 kg/m². Which of the following is the most likely diagnosis?

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11ec160b_35ff_f160_9249_e3a67c17db2d_MD0001_00 This patient's low body weight, distorted body perception, and findings consistent with self-induced vomiting (pharyngeal erythema, parotid hypertrophy) are suggestive of anorexia nervosa. Significantly low body weight (BMI ≤18.5 kg/m² in adults) is a core feature of anorexia nervosa and is accompanied by a distorted body image and fear of weight gain. There are two subtypes of anorexia. In the restricting subtype, patients fast and exercise excessively but do not purge. In the binge eating/purging subtype, patients engage in vomiting and/or use substances (laxatives, enemas, or diuretics) to avoid weight gain. Findings on physical examination in AN include emaciation, bradycardia, hypotension, hypothermia, hair loss, dry skin, lanugo (fine, downy body hair), and abdominal distension. In the purging subtype, hypokalemia and alkalosis are often present due to repetitive vomiting. (Choice B) In body dysmorphic disorder, patients display a preoccupation with a perceived or slight bodily defect. Dysmorphic disorder is not diagnosed when body distortion is accompanied by symptoms of an eating disorder (eg, low body weight, fear of weight gain). (Choice C) Discrete periods of uncontrollable eating, with subsequent compensatory behavior (laxatives, diuretics, vomiting, excessive exercise), occur in bulimia nervosa. However, patients with this condition have a normal or increased body weight (in comparison with AN in which weight is significantly decreased). (Choice D) Although constipation (hypoactive bowel sounds) and fatigue can also be seen in hypothyroidism, this patient's low weight, fear of gaining weight, distorted body image, and purging make anorexia nervosa more likely. (Choice E) Irritable bowel syndrome presents with chronic abdominal pain and altered bowel habits (diarrhea, constipation, or mixed-type). Patients often have abdominal bloating. This diagnosis would not explain signs of purging, distorted body image, and significantly low weight. (Choice F) This patient does not meet the diagnostic criteria for major depressive disorder. Her depressed mood, fatigue, and poor concentration are consistent with the effects of malnutrition. Educational objective: Anorexia nervosa is characterized by a distorted body image and fear of weight gain despite significantly low body weight. Patients may restrict their food intake and/or binge and purge. The key in distinguishing anorexia nervosa from bulimia nervosa is abnormally low body weight. __________ References: Initial evaluation, diagnosis, and treatment of anorexia nervosa and bulimia nervosa. (http://www.ncbi.nlm.nih.gov/pubmed/25591200) Less symptomatic, but equally impaired: clinical impairment in restricting versus binge-eating/purging subtype of anorexia nervosa. (http://www.ncbi.nlm.nih.gov/pubmed/29310054) Eating disorders in the primary care setting. (http://www.ncbi.nlm.nih.gov/pubmed/27262009)

A 20-Year-Old College Student Comes to the Office Due to Fatigue