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Anorexia Nervosa (AN)

Basics

  • Restriction of food intake causing low weight.
  • Intense fear of gaining weight.
  • Distorted perception of body weight and shape.
  • DSM-5 types:
  • Restricting type: no binge/purge in past 3 months.
  • Binge-eating/purging type: regular binge or purge behaviors in past 3 months.
  • Severity based on BMI (<15 kg/m² = severe).

Epidemiology

  • Lifetime prevalence ~0.5% among US adults.
  • Median onset age: 17 years.
  • Female predominance (10-20:1 female-to-male ratio).

Etiology & Pathophysiology

  • Multifactorial: genetic, biological, environmental, psychological, social.
  • Neurotransmitters: serotonin, norepinephrine, dopamine implicated.
  • Genetics: 11-fold increased risk in female relatives; higher concordance in monozygotic twins.
  • GWAS identified 8 significant loci.

Risk Factors

  • Body dissatisfaction, negative self-evaluation.
  • Perfectionism, high parental demands, academic stress.
  • History of abuse or maltreatment.
  • Activities emphasizing leanness (ballet, gymnastics).
  • Type 1 diabetes mellitus.
  • Family history of substance abuse, affective or eating disorders.

Diagnosis

DSM-5 Criteria

  • Restriction of energy intake leading to low weight.
  • Intense fear of weight gain or behavior preventing weight gain.
  • Distorted body image or denial of medical seriousness.

History

  • Insidious or stress-related onset.
  • Food restriction, elaborate rituals, excessive exercise.
  • Amenorrhea, fatigue, cold intolerance, GI symptoms.
  • Screening: SCOFF questionnaire.

Physical Exam

  • Vital sign abnormalities: hypothermia, bradycardia, orthostatic hypotension.
  • Body weight <85% expected (patients may hide true weight).
  • Signs: mitral valve prolapse, dry skin, lanugo, hair loss, peripheral edema, amenorrhea.

Differential Diagnosis

  • Hyperthyroidism, adrenal insufficiency.
  • IBS, malabsorption.
  • Immunodeficiency, chronic infections.
  • Bulimia, body dysmorphic disorder.
  • Depressive, anxiety, conversion disorders.

Diagnostic Tests

  • CBC: anemia, leukopenia, thrombocytopenia.
  • Electrolytes: hyponatremia, hypokalemia, hypophosphatemia, hypomagnesemia.
  • Thyroid function: low TSH with normal T3/T4.
  • LFTs abnormal.
  • ECG: prolonged QT interval.
  • DEXA scan: for bone density if chronic low weight.

Treatment

General Measures

  • Outpatient for medically stable, motivated patients.
  • Interdisciplinary approach: primary care, mental health, dietitian.
  • Gradual weight gain goal: 0.5 to 1 kg/week.
  • Cognitive behavioral therapy (CBT) focused on health, trust, emotional triggers.
  • Inpatient for instability, comorbid psychosis, inability to control behaviors.
  • Monitor for refeeding syndrome.
  • Stepwise activity increase.
  • Tube feeding/TPN as last resort.

Medication

  • No FDA-approved meds for AN; pharmacotherapy adjunctive.
  • SSRIs: relapse prevention, comorbid depression/OCD.
  • Atypical antipsychotics (e.g., olanzapine) studied with mixed results.
  • Avoid bupropion (seizure risk).
  • Manage osteopenia with calcium/vitamin D; bisphosphonates generally not indicated.
  • Psyllium for constipation.

Referral

  • Interdisciplinary team essential.
  • Specialized eating disorder programs.

Admission Criteria

  • Physiologic: HR <40 bpm, BP <90/60, hypoglycemia, hypothermia, dehydration, weight <75% expected.
  • Psychological: poor motivation, suicidal ideation, inability to eat, severe psych comorbidity.
  • Lab: K+ <3 mmol/L, prolonged QTc >0.499 sec, abnormal urine specific gravity.

Prognosis

  • 50% recover, 30% improve, 20% chronic illness.
  • Mortality 5-18%, high suicide risk (~20% of deaths).
  • Complications: refeeding syndrome, cardiac arrhythmias, osteoporosis, neurologic deficits.

Pregnancy

  • Risk of preterm labor, low birth weight infants.
  • Manage as high risk.

Clinical Pearls

  • Screening with simple questions helps early identification.
  • High suicide risk necessitates careful monitoring.
  • Combined psychotherapy and medical management improves outcomes.