Definition and Core Concepts

Eating disorders (EDs) are psychiatric conditions characterized by severe body dissatisfaction, overvaluation of a thin body ideal, and dysfunctional cognitive and weight control behaviors.
Anorexia nervosa (AN) typically affects 15 to 19-year-old girls and involves a significant overestimation of body size and shape, coupled with a relentless pursuit of thinness.
AN presents with an intense fear of becoming fat despite the patient being significantly underweight (often body weight <85% of expected).
Bulimia nervosa (BN) generally affects 10 to 19-year-old youth (chiefly females) and tends to emerge in later adolescence, sometimes evolving directly from preexisting AN.
BN is characterized by recurrent episodes of binge eating alternating with inappropriate compensatory behaviors, such as self-induced vomiting, misuse of laxatives or diuretics, fasting, or excessive exercise.
While AN involves extreme loss of weight, the weight of individuals with BN may fluctuate around a normal to moderately high baseline.

Epidemiology and Patient Profile

Feature	Anorexia Nervosa	Bulimia Nervosa
Typical Onset	Early to middle adolescence (15–19 years).	Later adolescence (10–19 years).
Personality Traits	Above-average intelligence, perfectionist, conflict-avoidant, and risk-aversive.	High impulsivity and frequent features of borderline personality disorder.
Psychiatric Comorbidities	High rates of anxiety, obsessive-compulsive symptoms, and emotional "numbness" to starvation.	Pronounced mood swings, depression, Post Traumatic Stress Disorder (PTSD), and higher risk of suicidal ideation.

DSM-5 Diagnostic Criteria

Diagnostic Domain	Anorexia Nervosa	Bulimia Nervosa
Core Behaviors	Restriction of energy intake relative to requirements, leading to significantly low body weight.	Recurrent episodes of binge eating (eating large amounts with a sense of lack of control).
Cognitive Features	Intense fear of gaining weight or becoming fat, and severe disturbance in body weight/shape perception.	Self-evaluation is unduly influenced by body shape and weight.
Compensatory Acts	Persistent behavior interfering with weight gain despite being at a significantly low weight.	Recurrent inappropriate compensatory behaviors (vomiting, laxatives, exercise) to prevent weight gain.
Timeframe/Frequency	Continuous restrictive behaviors causing persistent significantly low weight.	Binge eating and compensatory behaviors occur at least once a week for 3 months.
Subtypes	Restricting type (weight loss via fasting/dieting/exercise); Binge-eating/purging type.	N/A (Severity is based on the number of compensatory episodes per week).

Types of Anorexia Nervosa

According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), Anorexia Nervosa (AN) is classified into two primary subtypes based on the predominant behaviors exhibited by the patient during the preceding three months:

1. Restricting Type

Mechanism: Weight loss is accomplished primarily through severe caloric restriction (dieting, fasting) and/or excessive, compulsive exercise.
Behavioral Characteristics: The patient has not engaged in recurrent episodes of binge eating or purging behavior over the last 3 months.
Clinical Profile: Often associated with highly perfectionistic traits, rigid adherence to rules, social withdrawal, and profound obsessionality regarding food, caloric intake, and body shape.

2. Binge-Eating/Purging Type

Mechanism: The patient engages in recurrent episodes of binge eating, purging behavior, or both.
Purging Behaviors: Includes self-induced vomiting, or the inappropriate use of laxatives, diuretics, or enemas to compensate for caloric intake or ease anxiety after eating.
Clinical Profile: Associated with higher rates of impulsivity, emotional lability, and substance use. These patients are at a higher risk for acute medical complications (e.g., severe electrolyte imbalances like hypokalemia, metabolic alkalosis, dental enamel erosion, parotid gland hypertrophy) compared to the restricting type.

3. Atypical Anorexia Nervosa (OSFED)

Clinically relevant but formally categorized under Other Specified Feeding or Eating Disorders (OSFED) in DSM-5.
Criteria: All psychological and behavioral criteria for AN are met; however, despite significant and rapid weight loss, the individual's current weight remains within or above the normal range.

Comparison of Eating and Weight Control Habits

Habit	Anorexia Nervosa	Bulimia Nervosa
Dieting and Intake	Rigid adherence to "rules," monotonous "good" food choices, and progressive caloric restriction.	Chaotic eating; frequent dieting interspersed with impulsive, unregulated overeating.
Meals and Snacks	Consistent schedule; snacks and meals (especially breakfast) are reduced or eliminated.	Meals are less regimented and often eliminated following a binge-purge episode; snack comfort foods trigger binges.
Binge Eating	Absent in the restrictive subtype; an essential feature only in the binge-purge subtype.	An essential, often secretive feature associated with strong shame and guilt.
Purging Behaviors	Laxatives may be used to relieve constipation in the restrictive subtype.	Vomiting and laxatives are used frequently as cathartics to reduce the effects of overeating.
Exercise	Characteristically obsessive-compulsive, ritualistic, and progressive.	Less predictable; exercise may be avoided entirely or used as a means of purging.

Physical Signs and Medical Complications

System	Anorexia Nervosa	Bulimia Nervosa
General & Metabolic	Cachexia, hypothermia (<35.5°C), cold intolerance, hypoglycemia, and metabolic acidosis/alkalosis.	Weight variable; hypometabolic state less common, but high risk for hypokalemia and electrolyte imbalances.
Cardiovascular	Sinus bradycardia, hypotension, orthostasis, and low ECG voltage.	Palpitations, hypovolemia, and dangerous cardiac arrhythmias secondary to electrolyte disturbances.
Dermatologic & Hair	Dry and scaly skin, lanugo hair growth on face/body, alopecia, and acrocyanosis.	Calluses over proximal knuckle joints (Russell sign) from digital pharyngeal stimulation.
Oral & Gastrointestinal	Early satiety, gastric atony, and severe constipation.	Dental enamel erosion (perimolysis), parotid gland enlargement, subconjunctival hemorrhage, and esophageal ulceration.
Endocrine & Skeletal	Amenorrhea (preceding weight loss in up to 30%), delayed puberty, osteopenia, and osteoporosis.	Irregular menses; osteopenia is generally less pronounced than in AN.

Differential Diagnosis

Clinicians must rule out medical conditions presenting with high catabolism, such as hyperthyroidism, occult chronic infections, and malignancies.
Malabsorption syndromes like celiac disease or inflammatory bowel disease can mimic the weight loss of EDs; however, eating in AN causes discomfort due to gastric atony rather than true malabsorption.
Endocrine disorders such as Addison disease mimic the symptoms of restrictive AN but distinctly present with hyperkalemia and hyperpigmentation.
Central nervous system anomalies, including craniopharyngiomas or Rathke pouch tumors, may cause weight loss and growth failure but present with signs of increased intracranial pressure.
Mitochondrial neurogastrointestinal encephalomyopathy (caused by a TYMP gene mutation) presents with gastrointestinal dysmotility, cachexia, and leukoencephalopathy, and is frequently misdiagnosed initially as AN.
Avoidant/restrictive food intake disorder (ARFID) mimics AN's severe weight loss but lacks any underlying disturbance in body image or drive for thinness; the restriction is driven by sensory aversions or fears of choking.

Management Principles

The treatment of both AN and BN is ideally provided by an interdisciplinary team comprising a physician, nurse, registered dietitian, and mental health provider.
The approach should utilize the biopsychosocial model, framing the ED as a "maladaptive coping mechanism" and avoiding placing blame on the patient or the parents.
Nutritional Rehabilitation (AN):
- The initial goal is to achieve steady weight gain (0.25-0.5 kg/week) by increasing energy intake by 100–200 kcal increments toward a target of approximately 90% of expected body weight.
- Refeeding must proceed carefully, monitoring for refeeding syndrome (characterized by rapid drops in serum phosphorus, magnesium, and potassium) which can precipitate tachycardia, heart failure, and neurologic symptoms.
- Fat content may initially need to be lowered to 15–20% to accommodate fat phobia, alongside calcium and vitamin D supplementation to address osteopenia.
Inpatient Medical Hospitalization (AN): Indicated for physiological instability, including a heart rate <50 beats/min, blood pressure <80/50 mm Hg, profound hypothermia (<36.1°C), severe electrolyte disturbances, or body weight <80% of healthy expected weight.
Psychotherapy:
- Family-Based Treatment: The Maudsley approach is the only evidence-based treatment for AN in children and adolescents; it empowers parents to take an active, nurturing role in restoring their child's eating habits without blame.
- Cognitive-Behavioral Therapy (CBT): Focuses on restructuring thinking errors and establishing adaptive behaviors; it is highly effective in treating both AN and BN.
- Dialectical Behavioral Therapy (DBT): Specifically useful for older adolescents with BN to challenge distorted thoughts and improve emotion regulation and mindfulness.
Pharmacotherapy:
- Selective Serotonin Reuptake Inhibitors (SSRIs) lack evidence of efficacy for patients with AN who are at a low weight; nutritional restoration remains the primary treatment for depression in AN.
- Conversely, SSRIs (such as fluoxetine at equivalent doses of >60 mg) are considered a standard element of therapy for BN and are highly effective in reducing binge-purge behaviors regardless of the presence of depression.