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Difficulty: MediumSomatic Symptom and Eating Disorders

A 16-year-old girl is evaluated in the outpatient clinic for primary amenorrhea. She has never had a menstrual period. Over the past year, she has become increasingly focused on maintaining a 'clean' lifestyle, strictly eliminating fats and carbohydrates from her diet, and exercising for at least two hours daily. Her mother reports that the patient often complains of feeling cold and fatigued but continues to excel academically. The patient takes no medications and denies sexual activity. Her temperature is 35.8°C (96.4°F), blood pressure is 92/58 mm Hg, and pulse is 48/min. Her BMI is 15.2 kg/m². Physical examination reveals fine, soft hair on her back and abdomen, as well as dry skin. Pelvic examination is normal. Laboratory testing reveals:

Laboratory TestResultReference Range
Beta-hCGNegativeNegative
FSH3 mIU/mL4.0 - 10.0 mIU/mL
LH1 mIU/mL2.0 - 15.0 mIU/mL
TSH2.1 µU/mL0.5 - 5.0 µU/mL
Free T41.1 ng/dL0.9 - 1.7 ng/dL
Total T355 ng/dL80 - 200 ng/dL

Which of the following is the most likely diagnosis?

  1. Anorexia nervosaAnswer
  2. B
    Primary hypothyroidism
  3. C
    Bulimia nervosa
  4. D
    Polycystic ovary syndrome
  5. E
    Constitutional delay of growth and puberty

Answer

Anorexia nervosa
The correct answer is anorexia nervosa. This patient presents with the classic triad of an eating disorder: restricted energy intake, fear of weight gain, and distorted body image (implied by her rigid 'clean' eating and excessive exercise despite being severely underweight). Her BMI of 15.2 kg/m² categorizes her eating disorder strictly as anorexia nervosa. The systemic complications of starvation are evident in her vital signs (bradycardia, hypothermia) and physical exam (lanugo). Furthermore, her laboratory results show the expected endocrine adaptations to starvation: functional hypothalamic amenorrhea (decreased GnRH leading to low FSH and LH, resulting in absent menarche) and euthyroid sick syndrome (decreased peripheral conversion of T4 to T3 to lower the basal metabolic rate, yielding a low T3 with normal TSH and Free T4).

Step-by-Step Solution

1
Analyze the clinical presentation and vital signs.
The patient is a 16-year-old with primary amenorrhea, restrictive dietary habits, excessive exercise, profound underweight status (BMI 15.2), bradycardia, hypothermia, and lanugo.
Identifying the clinical syndrome of starvation and excessive energy deficit points toward an eating disorder.
2
Interpret the laboratory findings.
Low FSH and LH indicate functional hypothalamic amenorrhea. Normal TSH and Free T4 with a low T3 indicates euthyroid sick syndrome.
These endocrine abnormalities are physiological adaptations to severe caloric restriction and weight loss, confirming a central suppression rather than a primary organ failure.
3
Differentiate between eating disorders based on diagnostic criteria.
The defining feature distinguishing this presentation from bulimia nervosa is the severely low BMI (< 18.5 kg/m²).
A diagnosis of anorexia nervosa requires restriction of energy intake leading to a significantly low body weight, which perfectly matches this patient's presentation.

Key Concept

Patients with anorexia nervosa frequently present with systemic complications of starvation, including functional hypothalamic amenorrhea (low FSH/LH) and euthyroid sick syndrome (low T3 with normal TSH/T4), alongside physical signs like bradycardia, hypothermia, and lanugo.
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Topics

Somatic Symptom and Eating Disorders

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