Restriction of intake leading to significantly low body weight, intense fear of weight gain, and disturbed body image.
Also known as: anorexia, anorexia nervosa, restrictive eating disorder
Overview
An eating disorder characterized by restriction of energy intake leading to significantly low body weight relative to age, sex, developmental trajectory, and physical health; intense fear of gaining weight or persistent behavior interfering with weight gain; and disturbance in the way one's body weight or shape is experienced.
Epidemiology
Lifetime prevalence ~1% in women, ~0.3% in men. Peak onset adolescence/young adulthood. Highest mortality of any psychiatric disorder (~5-6x age-matched controls).
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Question 1PsychiatryMedium
A 14-year-old female is brought by her mother for restriction of food intake, fear of weight gain, and BMI of 16.5 kg/m² (below 5th percentile for age). She exercises 3 hours daily. She denies body image disturbance when asked directly but is intensely focused on healthy eating. Vital signs show HR 44 bpm. Labs show hypokalemia (K+ 3.4 mEq/L), low estrogen, and elevated BUN (32 mg/dL). Which of the following findings is the most concerning and requires immediate medical attention?
ABradycardia (HR 44 bpm)
BElevated BUN (32 mg/dL)
CBMI 16.5 kg/m²
DHypokalemia (K+ 3.4 mEq/L)
Reveal answer & full explanation
Correct answer: A — Bradycardia (HR 44 bpm)
ABradycardia (HR 44 bpm)✓
BElevated BUN (32 mg/dL)
CBMI 16.5 kg/m²
DHypokalemia (K+ 3.4 mEq/L)
Why Bradycardia (HR 44 bpm) is correct
Cardiac complications are the most common cause of death in anorexia nervosa (arrhythmias and myocardial atrophy from protein-energy malnutrition).
Bradycardia (HR below 50 bpm) is a criterion for inpatient medical stabilization, driven by autonomic dysfunction from starvation and increased vagal tone.
HR 44 falls well below the admission threshold and reflects hemodynamic instability warranting continuous cardiac monitoring.
ECG changes include prolonged QTc (electrolyte-driven), ST-T changes, and ventricular arrhythmias.
Why the others are wrong
BMI 16.5 kg/m² — right-concept-wrong-threshold: low BMI is a component of severity assessment, but medical admission is triggered at BMI below 15 or a rapidly declining trend, so 16.5 is not itself an immediate admission criterion.
Elevated BUN (32 mg/dL) — prerenal azotemia from volume depletion; it corrects with rehydration, is not a medical admission criterion on its own, and is far less immediately dangerous than the arrhythmia risk posed by HR 44.
Hypokalemia (K+ 3.4 mEq/L) — anchoring on "abnormal electrolyte": hypokalemia is an admission criterion only when K+ is below 3.0; at 3.4 it is mildly low and far less immediately dangerous than the arrhythmia risk posed by HR 44.
Additional high-yield points
Medical admission criteria: HR below 50 or above 110, BP below 90/60, orthostatic hypotension (above 20 mmHg drop), QTc above 450 ms, glucose below 60, K+ below 3.0, severe electrolyte imbalance, BMI below 15 or rapidly declining, syncope, acute medical complications.
Refeeding syndrome (hypophosphatemia, hypomagnesemia, hypokalemia) — prevent with thiamine plus daily monitoring and repletion of phosphate, potassium, and magnesium; with that monitoring, higher-calorie starts (about 1500-2000 kcal/day) advanced quickly are supported in mild-moderate malnutrition (SAHM 2022).
Pharmacotherapy: low-dose olanzapine may improve weight gain and reduce eating-related anxiety; selective serotonin reuptake inhibitors (SSRIs) are ineffective during malnutrition.
Family-based treatment (FBT) (Maudsley) is the most effective psychotherapy for adolescent anorexia nervosa (AN).
Question 2PsychiatryMedium
A 16-year-old girl is brought by her parents with progressive food restriction, fear of weight gain, and amenorrhea for 4 months. BMI is 15.8 kg/m². Labs show hypokalemia (K 3.0), metabolic alkalosis, and elevated amylase. Her teeth show enamel erosion. Which of the following best explains the hypokalemia and elevated amylase?
ADiuretic abuse
BSelf-induced vomiting
CSevere dietary restriction alone
DExcessive exercise
ELaxative abuse
Reveal answer & full explanation
Correct answer: B — Self-induced vomiting
ADiuretic abuse
BSelf-induced vomiting✓
CSevere dietary restriction alone
DExcessive exercise
ELaxative abuse
Why Self-induced vomiting is correct
This presentation is anorexia nervosa, binge-eating/purging type; bulimia nervosa is not diagnosed when the behavior occurs only during anorexia nervosa (DSM-5-TR criterion E).
Hypokalemia + metabolic alkalosis + elevated amylase (parotid gland hypertrophy from repeated vomiting) + dental enamel erosion from acid are all hallmarks of purging behavior (self-induced vomiting).
Russell's sign (calluses on dorsum of hand from teeth during self-induced vomiting) is another classic finding.
Why the others are wrong
Laxative abuse — Laxative abuse causes hypokalemia but produces non-anion gap metabolic acidosis (not alkalosis) and secretory diarrhea.
Severe dietary restriction alone — Restriction alone does not explain amylase elevation or metabolic alkalosis.
Excessive exercise — Excessive exercise does not account for the metabolic alkalosis, elevated amylase, or enamel erosion seen here.
Diuretic abuse — diuretic misuse is the classic look-alike because it also causes hypokalemia with metabolic alkalosis, but it does not stimulate the parotid glands or erode dental enamel; salivary-type hyperamylasemia from parotid enlargement and acid erosion of the teeth point specifically to repeated vomiting.
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Family history of eating, mood, or anxiety disorders
Perfectionistic, anxious, or obsessional temperament
Cultural and athletic pressures emphasizing thinness (dance, gymnastics, wrestling, running)
Early menarche
Type 1 diabetes ('diabulimia')
Pathophysiology
Polygenic vulnerability with disturbed reward processing, altered serotonergic signaling, and structural/functional changes in insular and frontal cortices. Starvation itself perpetuates rigid cognition and physiologic adaptations.
Clinical presentation
Symptoms
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
Bulimia nervosa — Binge-purge cycles with normal or above-normal weight
Avoidant/restrictive food intake disorder (ARFID) — Low intake without body image disturbance — sensory aversion, fear of aversive consequences, lack of interest
Body dysmorphic disorder — Preoccupation with appearance flaw not centered on weight
Medical causes of weight loss — Hyperthyroidism, IBD, malignancy, T1DM, celiac, Addison — workup if behavioral history atypical
MDD with poor appetite — Weight loss secondary to anhedonia; body image not distorted
Diagnostic workup
Diagnostic criteria
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 self-evaluation, or lack of recognition of seriousness of low weight. Severity by BMI: mild >=17, moderate 16-16.99, severe 15-15.99, extreme <15. Subtype: restricting vs binge-eating/purging.
Nutritional rehabilitation with structured meal plan and gradual weight restoration
Medical hospitalization for severe malnutrition, hemodynamic instability, electrolyte derangement, suicidality
Second-line / adjunct
Olanzapine — modest evidence for weight restoration and obsessional thinking in adults
SSRIs only for treating comorbid depression/anxiety — NOT effective for core anorexia symptoms in low-weight state
Residential or partial hospitalization programs
Bisphosphonates considered for low bone density only in select cases
Complications
Refeeding syndrome — hypophosphatemia, hypokalemia, hypomagnesemia, thiamine deficiency, fluid shifts; cardiac failure and arrhythmia; insulin released when carbohydrate is reintroduced drives PO4, K and Mg into cells, so hypophosphatemia is the hallmark; risk tracks the degree of malnutrition (e.g., BMI <16 or <70% of median BMI), negligible intake >10 days, and low pre-feeding PO4, K or Mg; with daily electrolyte monitoring, many programs now start around 1500-2000 kcal/day and advance quickly in mild-moderate malnutrition (SAHM 2022), while the most severely malnourished, highest-risk patients may start lower and advance more cautiously; replete electrolytes proactively
Cardiac (leading medical cause of death): bradycardia, prolonged QT, pericardial effusion, cardiomyopathy, sudden cardiac death
Endocrine: amenorrhea, hypothalamic hypogonadism, infertility, low bone density
GI: gastroparesis, constipation, SMA syndrome
Renal calculi, electrolyte disturbances
Suicide (~20% of mortality)
PANCE pearls
Hospitalization criteria (one or more; APA 2023, SAHM 2022): HR <50 (SAHM: <50 daytime or <45 at night); BP <90/45; orthostatic HR rise >30 in adults or >40 in adolescents, or BP drop >20 systolic or >10 diastolic; temp <35.6C (96F); hypoglycemia; hypokalemia (e.g., K <3), hyponatremia, hypophosphatemia, or hypomagnesemia; QTc >450 or arrhythmia; BMI <15 in adults or <=75% of median BMI in adolescents; acute food refusal or uncontrolled bingeing and purging; syncope, seizure, heart failure, or pancreatitis; suicidality or failure of outpatient treatment.
Refeeding syndrome occurs in first 1-2 weeks — check phosphate, magnesium, potassium daily; supplement thiamine BEFORE refeeding.
Bone density loss is largely irreversible — weight restoration is the most important intervention; combined OCPs do NOT improve bone density and their withdrawal bleeds can falsely reassure; a physiologic transdermal 17-beta estradiol patch with cyclic progestin may be considered when low BMD persists despite attempted weight restoration.
Family-based treatment outperforms individual therapy in adolescents — engage parents as agents of refeeding.
References
APA 2023 — American Psychiatric Association Practice Guideline for the Treatment of Patients with Eating Disorders, 4th ed. (2023)
AED 2021 — Academy for Eating Disorders Medical Care Standards Committee. Eating Disorders: A Guide to Medical Care, 4th ed. AED Report 2021.
DSM-5-TR — American Psychiatric Association. DSM-5-TR (2022)
SAHM 2022 — Society for Adolescent Health and Medicine. Medical management of restrictive eating disorders in adolescents and young adults. J Adolesc Health. 2022;71(5):648-654.
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