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Zorluk: ZorSomatic Symptom and Eating Disorders

An accompanying friend brings a 2323-year-old female ballet dancer to the emergency department after the patient experienced an episode of syncope during a rehearsal. The friend notes that the patient has been increasingly obsessed with her weight, often skipping meals and expressing intense fear of becoming overweight despite appearing remarkably thin. Her current body mass index is 17.1 kg/m217.1 \text{ kg/m}^2.

On physical examination, blood pressure is 86/52 mmHg86/52 \text{ mmHg} and heart rate is 114/min114/\text{min}. Tapping over the facial nerve elicits a twitch of the nose and lips.

Initial laboratory studies reveal:

Laboratory TestResultReference Range
Sodium133 mEq/L133 \text{ mEq/L}136−145 mEq/L136-145 \text{ mEq/L}
Potassium2.2 mEq/L2.2 \text{ mEq/L}3.5−5.0 mEq/L3.5-5.0 \text{ mEq/L}
Chloride80 mEq/L80 \text{ mEq/L}95−105 mEq/L95-105 \text{ mEq/L}
Bicarbonate39 mEq/L39 \text{ mEq/L}22−28 mEq/L22-28 \text{ mEq/L}
Blood urea nitrogen42 mg/dL42 \text{ mg/dL}7−18 mg/dL7-18 \text{ mg/dL}
Creatinine1.5 mg/dL1.5 \text{ mg/dL}0.6−1.2 mg/dL0.6-1.2 \text{ mg/dL}
Ionized calcium3.6 mg/dL3.6 \text{ mg/dL}4.5−5.6 mg/dL4.5-5.6 \text{ mg/dL}
Magnesium1.0 mg/dL1.0 \text{ mg/dL}1.7−2.2 mg/dL1.7-2.2 \text{ mg/dL}

Arterial blood gas (room air):

ParameterResult
pH7.557.55
pCO2_249 mmHg49 \text{ mmHg}
pO2_294 mmHg94 \text{ mmHg}

Random urine studies:

TestResult
Urine chloride55 mEq/L55 \text{ mEq/L}

Which of the following is the most likely etiology of this patient's laboratory abnormalities?

  1. A
    Repeated mechanical induction of the oropharyngeal gag reflex
  2. B
    Inadequate respiratory compensation for a primary metabolic derangement
  3. Pharmacological inhibition of the thick ascending limb sodium-potassium-chloride cotransporterCevap
  4. D
    Surreptitious administration of intestinal peristalsis-stimulating agents
  5. E
    Prolonged fasting leading to systemic accumulation of beta-hydroxybutyrate

Cevap

The correct etiology is the pharmacological inhibition of the thick ascending limb sodium-potassium-chloride cotransporter (covert loop diuretic abuse).
The correct answer describes the mechanism of action of loop diuretics, which inhibit the Na +^+-K +^+-22 Cl −^- cotransporter in the thick ascending limb of the loop of Henle. This patient, an elite dancer with body image distortion and a remarkably low BMI, suffers from an eating disorder. Her presentation of hypokalemia, hypochloremia, and profound metabolic alkalosis points to a purging mechanism. The critical distinguishing factor is her elevated random urine chloride (55 mEq/L55 \text{ mEq/L}). While vomiting (another common purging method) causes metabolic alkalosis, it is associated with a low urine chloride (<20 mEq/L<20 \text{ mEq/L}) because the functioning kidneys avidly reabsorb sodium and chloride to restore intravascular volume. In contrast, active diuretic use blocks chloride reabsorption, leading to high urine chloride despite systemic hypovolemia (evidenced by her elevated BUN/creatinine ratio). Furthermore, loop diuretics increase calcium excretion, explaining her hypocalcemia and resulting tetany (Chvostek sign), whereas thiazides would typically cause hypercalcemia.

Adım Adım Çözüm

1
Analyze the arterial blood gas and serum electrolyte values.
The patient has a primary metabolic alkalosis (pH 7.557.55, HCO 3−_3^- 39 mEq/L39 \text{ mEq/L}) with appropriate respiratory compensation (pCO 2_2 49 mmHg49 \text{ mmHg}).
Establishing the primary acid-base disorder is the crucial first step in narrowing the differential diagnosis.
2
Evaluate the urine chloride concentration.
The urine chloride is elevated (55 mEq/L55 \text{ mEq/L}), indicating a saline-unresponsive etiology.
Urine chloride helps distinguish between volume-depleted states where the kidney reabsorbs chloride (e.g., vomiting, <20 mEq/L<20 \text{ mEq/L}) and states where chloride reabsorption is blocked (e.g., diuretic use, >20 mEq/L>20 \text{ mEq/L}).
3
Correlate physical findings and remaining electrolytes with the suspected etiology.
The hypocalcemia (3.6 mg/dL3.6 \text{ mg/dL}) causing Chvostek sign, along with hypomagnesemia, confirms the use of loop diuretics rather than thiazides.
Loop diuretics increase urinary calcium excretion, leading to hypocalcemia, whereas thiazide diuretics decrease urinary calcium excretion.

Anahtar Kavram

In patients with eating disorders, identifying the specific purging behavior relies on acid-base and electrolyte patterns. Loop diuretic abuse uniquely presents with hypokalemic, hypochloremic metabolic alkalosis, elevated urine chloride (>20 mEq/L>20 \text{ mEq/L}), and hypocalcemia.
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