A 21-year-old female university student is evaluated in the emergency department for sever… — USMLE Step 2 CK

A $21$ -year-old female university student is evaluated in the emergency department for severe muscle cramps, palpitations, and dizziness when standing. She says she has been overwhelmed by her coursework and admits to having episodes where she eats excessively large quantities of food in a short period. Following these episodes, she induces vomiting because she is terrified of gaining weight. Her body mass index is $22.5 \text{ kg/m}^2$ . Blood pressure is $98/60 \text{ mm Hg}$ supine and $82/50 \text{ mm Hg}$ upon standing. Heart rate is $105/\text{min}$ . Physical examination reveals bilateral painless swelling of the cheeks and callous formation on the dorsum of her right hand. Laboratory studies reveal the following:

Laboratory Test	Result	Reference Range
Sodium	$137 \text{ mEq/L}$	$136-145 \text{ mEq/L}$
Potassium	$2.6 \text{ mEq/L}$	$3.5-5.0 \text{ mEq/L}$
Chloride	$86 \text{ mEq/L}$	$98-106 \text{ mEq/L}$
Bicarbonate	$37 \text{ mEq/L}$	$22-28 \text{ mEq/L}$
TSH	$1.2 \text{ \mu U/mL}$	$0.4-4.0 \text{ \mu U/mL}$
Free T4	$0.9 \text{ ng/dL}$	$0.9-1.7 \text{ ng/dL}$
Free T3	$65 \text{ ng/dL}$	$80-200 \text{ ng/dL}$

Arterial blood gas on room air:

Parameter	Result
pH	$7.53$
pCO $_2$	$48 \text{ mm Hg}$
pO $_2$	$92 \text{ mm Hg}$

In addition to acute intravenous fluid and electrolyte resuscitation, which of the following is the most appropriate step in the management of this patient's condition?

Initiation of fluoxetine to reduce the frequency of binge-eating and purging episodesCevap
B
Prescription of bupropion to manage underlying mood symptoms without causing weight gain
C
Initiation of noninvasive positive pressure ventilation to address the primary respiratory acidosis
D
Administration of levothyroxine to treat secondary hypothyroidism causing her fatigue
E
Initiation of antipsychotic therapy to manage her distorted and fixed beliefs about her body weight

Cevap

The most appropriate long-term management step is the initiation of fluoxetine to reduce the frequency of binge-eating and purging episodes.

The patient's presentation of binge eating, self-induced vomiting, normal body mass index (

22.5 \text{ kg/m}^2

), parotid swelling, and Russell sign confirm a diagnosis of bulimia nervosa. Her labs reflect severe hypokalemic, hypochloremic metabolic alkalosis, a direct result of gastric acid and volume loss. Alongside nutritional rehabilitation and psychotherapy (Cognitive Behavioral Therapy), Selective Serotonin Reuptake Inhibitors (SSRIs) are the pharmacologic treatment of choice. Fluoxetine is FDA-approved for bulimia nervosa and has been proven to significantly decrease both binge-eating and purging frequencies, regardless of comorbid depression.

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Diagnose the primary psychiatric condition based on clinical presentation.

The patient has Bulimia Nervosa, evidenced by recurrent binge eating, compensatory purging (self-induced vomiting), normal BMI, parotid gland enlargement, and Russell sign (calluses on knuckles).

Establishing the correct diagnosis distinguishes bulimia nervosa from anorexia nervosa, which typically presents with significantly low body weight (BMI < 18.5).

Interpret the laboratory and arterial blood gas findings.

The patient has severe hypokalemic, hypochloremic metabolic alkalosis (pH 7.53, high HCO3). The pCO2 of 48 is expected respiratory compensation (Expected pCO2 = 40 + [0.7 * (37 - 24)] = 49.1). The thyroid panel shows euthyroid sick syndrome.

Understanding the systemic complications of purging allows the clinician to avoid inappropriate interventions for expected compensatory mechanisms and lab anomalies.

Select the safest and most effective long-term pharmacotherapy.

Fluoxetine is selected as it is the first-line SSRI for bulimia nervosa. Bupropion is contraindicated due to seizure risk.

After acute medical stabilization of electrolytes and volume depletion, long-term pharmacological management alongside cognitive behavioral therapy is required to prevent relapse.

Anahtar Kavram

Bulimia nervosa is characterized by binge eating and compensatory behaviors at a normal or overweight BMI. Treatment involves nutritional rehabilitation, cognitive behavioral therapy, and SSRIs (specifically fluoxetine). Bupropion is contraindicated due to seizure risk.

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