What medical and non‑psychiatric conditions must be excluded before diagnosing anorexia nervosa?

Medical Conditions to Exclude Before Diagnosing Anorexia Nervosa

Before diagnosing anorexia nervosa, you must systematically rule out organic medical diseases that cause weight loss, including malignancies, inflammatory bowel disease, infections, metabolic disorders, and gastrointestinal dysmotility syndromes. 1

Essential Medical Workup

Laboratory Assessment

• Complete blood count (CBC) to detect anemia, leukopenia, or thrombocytopenia that may indicate underlying malignancy or systemic disease 2
• Comprehensive metabolic panel to identify electrolyte abnormalities, liver dysfunction, renal impairment, or metabolic disorders 2
• Thyroid function tests to exclude hyperthyroidism as a cause of weight loss and hypermetabolism 1

Cardiac Evaluation

• Electrocardiogram (ECG) is mandatory for all patients with restrictive eating patterns to detect arrhythmias or QTc prolongation that could indicate either cardiac complications or underlying cardiac disease 2

Gastrointestinal Disorders to Exclude

Inflammatory bowel disease (Crohn's disease, ulcerative colitis) must be ruled out, as these conditions present with weight loss, abdominal pain, and food avoidance but lack the body image distortion and fear of weight gain characteristic of anorexia nervosa 1

Small intestinal dysmotility syndromes can mimic anorexia nervosa presentation:

• Delayed gastric emptying and delayed small/large bowel transit occur in both anorexia nervosa and primary dysmotility disorders 3
• Superior mesenteric artery syndrome (Wilkie's syndrome) presents with postprandial epigastric pain, nausea, vomiting, and weight loss—symptoms that overlap significantly with anorexia nervosa 3
• The critical distinction: patients with primary dysmotility lack the intense fear of weight gain, body image distortion, and persistent behavior interfering with weight gain 3

Malignancies

Any form of cancer can cause significant weight loss through increased metabolic demands, anorexia, or mechanical obstruction 1. A thorough review of systems and age-appropriate cancer screening is essential before attributing weight loss to an eating disorder.

Infectious Diseases

Chronic infections (tuberculosis, HIV, parasitic infections) must be excluded as they cause progressive weight loss without the psychological features of anorexia nervosa 1

Endocrine and Metabolic Disorders

• Hyperthyroidism causes weight loss despite normal or increased appetite 1
• Diabetes mellitus (particularly type 1) can present with weight loss
• Adrenal insufficiency causes weight loss, fatigue, and electrolyte abnormalities 1

Psychiatric Conditions to Differentiate

Other Eating Disorders

Avoidant/restrictive food intake disorder (ARFID) presents with food restriction and weight loss but lacks body image distortion and fear of weight gain—the hallmark features that distinguish anorexia nervosa 3

Major Psychiatric Disorders

• Major depression can cause appetite loss and weight loss but without the specific body image concerns of anorexia nervosa 1
• Schizophrenia may involve food refusal due to delusions or paranoia rather than fear of weight gain 1
• Substance use disorders (particularly stimulants) cause weight loss through appetite suppression and should be identified through comprehensive substance use history 4, 1
• Anxiety disorders may involve food avoidance but lack the characteristic weight and shape preoccupation 1

Critical Diagnostic Algorithm

1. Obtain comprehensive weight history: document highest and lowest weights, rate of weight loss, and intentionality of restriction 2

2. Assess for DSM-5 anorexia nervosa criteria:

   • Persistent energy restriction leading to significantly low body weight
   • Intense fear of weight gain OR persistent behavior interfering with weight gain
   • Body image disturbance OR lack of recognition of seriousness of low weight 3

3. If psychiatric criteria are met, still complete medical workup to exclude organic causes that may coexist or be misattributed 1, 5

4. Perform targeted testing based on clinical presentation:

   • If gastrointestinal symptoms predominate: consider gastric emptying studies, imaging for superior mesenteric artery syndrome 3
   • If systemic symptoms present: expand infectious and malignancy workup 1

Common Pitfalls to Avoid

Do not assume weight loss is purely psychiatric without completing the medical workup—organic diseases can present with food avoidance that mimics eating disorder behavior 1, 5

Do not overlook functional gastrointestinal disorders that may coexist with or be confused for anorexia nervosa, particularly when significant malnutrition is absent despite prominent gastrointestinal symptoms 3

Recognize that malnutrition itself impairs gut function, causing delayed gastric emptying, mucosal atrophy, and bacterial overgrowth—these are consequences of starvation, not necessarily primary gastrointestinal disease 3

Be cautious with patients who have normal or high BMI but report restrictive eating—escalating to invasive nutritional interventions in the absence of objective biochemical disturbances risks iatrogenic harm, particularly if underlying functional symptoms or psychiatric conditions are the primary issue 3