What is the best course of treatment for a 19-year-old female with unexplained weight loss and decreased appetite?

Urgent Evaluation for Anorexia Nervosa in a 19-Year-Old Female

This 19-year-old female with unexplained weight loss and decreased appetite requires immediate assessment for anorexia nervosa with urgent evaluation of medical stability, followed by multidisciplinary treatment involving psychiatry, nutrition, and medical management. 1

Immediate Medical Assessment

Determine if hospitalization is required based on critical parameters:

• BMI <16 kg/m² mandates immediate hospitalization 1
• Heart rate <50 beats per minute during daytime or <45 beats per minute at night requires hospital admission 1
• Temperature <36.0°C (96.8°F) indicating hypothermia necessitates immediate intervention 1
• Orthostatic hypotension or orthostatic tachycardia suggesting cardiovascular compromise requires hospitalization 1
• QTc prolongation on ECG, particularly with purging behaviors, mandates hospital admission 1
• Severe electrolyte abnormalities posing immediate life threat require hospitalization 1

Differential Diagnosis Evaluation

Screen for eating disorder behaviors using validated measures when weight loss is unexplained:

• Evaluate for purging behaviors including vomiting, laxative abuse, and excessive exercise 1
• Screen for depression using age-appropriate validated measures, as depression commonly co-occurs with eating disorders 1
• Consider that inadvertent weight loss from medical illness, medication side effects, or life stressors can trigger anorexia nervosa in predisposed individuals 1
• Rule out diabetes by checking HbA1c, as severe hyperglycemia with catabolic features can cause unintentional weight loss 2
• Perform thyroid function tests (TSH) to evaluate for hyperthyroidism or hypothyroidism 2

Obtain urgent neuroimaging (MRI brain with contrast preferred) to exclude intracranial pathology in patients with significant weight loss 2

Treatment Approach for Confirmed Anorexia Nervosa

Implement a coordinated multidisciplinary treatment plan:

Nutritional Rehabilitation

• Set individualized goals for weekly weight gain and target weight 1
• Implement slow refeeding with possible phosphorus supplementation to prevent refeeding syndrome in severely malnourished patients 1
• The refeeding process requires close monitoring by a multidisciplinary medical team, as patient compliance is notoriously problematic 3
• Consider enteral feeding via nasogastric tube or percutaneous endoscopic gastrostomy for patients who refuse oral feeding or when oral therapy fails 4, 3

Psychiatric Management

• Address psychiatric comorbidities with evidence-based psychotherapy including cognitive behavioral therapy or interpersonal therapy 1
• The decision for involuntary treatment (if patient refuses) should be made by the primary physician after consultation with psychiatrists, medical specialists, and nutritionists 1
• Individual psychotherapy and family therapy are essential components of treatment 4

Pharmacological Considerations

For appetite stimulation if medically appropriate:

• Mirtazapine 7.5-15 mg at bedtime as first-line therapy, requiring 4-8 weeks for full therapeutic trial, with expected mean weight gain of 1.9 kg at 3 months 5
• Mirtazapine has dual benefit addressing both depression and appetite simultaneously, with approximately 80% of patients experiencing some weight gain 5
• Monitor for QTc prolongation with mirtazapine, especially in patients with cardiovascular disease or family history of QT prolongation 6
• Avoid second-generation antipsychotics like olanzapine in this population, as they increase risk of weight gain and metabolic complications 7

Prognostic Factors and Follow-Up

Poor prognostic indicators requiring more intensive intervention include:

• Illness duration exceeding 10 years 1
• BMI below 16 kg/m² 1
• Comorbid alcohol abuse 1
• Poor social adjustment 1

Prognosis is directly related to duration of illness, so early intervention is critical even when symptoms may be minimal 8. Despite multidisciplinary treatment efforts, only 40-50% of patients with anorexia nervosa progress to complete recovery 8.

Critical Pitfalls to Avoid

• Do not delay psychiatric referral while pursuing extensive medical workup if eating disorder is suspected 9
• Avoid aggressive refeeding in severely malnourished patients due to risk of refeeding syndrome 1
• Do not prescribe GLP-1 receptor agonists in patients with unexplained weight loss, as gastrointestinal side effects may worsen the condition 10
• Ensure close follow-up even if initial evaluation is normal, as up to 25% of patients with unintentional weight loss do not have a diagnosis after comprehensive workup 11