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Review Question - QID 104320

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QID 104320 (Type "104320" in App Search)
A 39-year-old female presents with confusion. Her husband reports that she doesn't know where she is and cannot remember the date. She was recently diagnosed with small cell lung cancer. Vital signs are T 37C, HR 80, BP 120/80 mmHg, RR 14, and O2 sat 99% on room air. She is not orthostatic. Physical examination reveals moist mucous membranes and normal capillary refill. A basic metabolic profile reveals that serum sodium is 129. Regarding this patient's illness, which of the following is true?

Urinary osmolarity will be > 100, and this illness will not correct with saline infusion

39%

36/92

Urinary osmolarity will be < 100, and another potential cause of this disorder is excessive water drinking

12%

11/92

Urinary sodium will be > 20 and fractional excretion of sodium will be >1%

37%

34/92

Urinary sodium will be < 10, and fractional excretion of sodium will be <1%

10%

9/92

Urinary sodium will be > 20 and another potential cause of this disorder is renal failure

1%

1/92

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The patient has a lung cancer causing ectopic release of ADH. In syndrome of inappropriate ADH (SIADH), patients have euvolemic hyponatremia, decreased serum osmolarity, elevated urine osmolarity, increased urine sodium concentration, and failure to correct with saline infusion.

Hyponatremia occurs when the body maintains excess water relative to sodium. It is almost always due to increased ADH, either appropriately secreted as in hypovolemia or hypervolemia with decreased effective arterial volume, or inappropriately as in SIADH. Hyponatremia should first be divided into hypovolemic causes (such as renal losses, mineralocorticoid deficiency, or extra renal losses), euvolemic (such as SIADH and primary polydipsia), and hypervolemic hyponatremia (secondary to CHF, cirrhosis, nephrosis, or renal failure). The differential is narrowed by assessing the volume status of the patient and then measuring urine and serum electrolytes.

Goh discusses management of hyponatremia. Hyponatremia is an important electrolyte abnormality with the potential for significant morbidity and mortality. Differentiating between euvolemia and hypovolemia can be clinically difficult, but a useful investigative aid is measurement of plasma osmolality. Hyponatremia with a high plasma osmolality is caused by hyperglycemia, while a normal plasma osmolality indicates pseudohyponatremia. The urinary sodium concentration helps in diagnosing patients with low plasma osmolality. In patients with chronic hyponatremia, fluid restriction is the mainstay of treatment, with demeclocycline therapy reserved for use in persistent cases.

Matsuura discusses hyponatremia in cancer patients. Hyponatremia is the most common electrolyte disturbance in cancer patients. Patients with extremely severe symptomatic hyponatremia need treatment with the administration of hypertonic saline. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a significant cause of cancer-related hyponatremia.Ectopic ADH production by malignant cells (especially in small-cell lung cancer), several anticancer drugs (cyclophosphamide, ifosfamide, vincristine, cisplatin), stress from surgery, pain, and nausea, may cause SIADH in cancer patients.

Illustration A depicts the breakdown of the different types of hyponatremia.

Incorrect Answers:
Answer 2: These factors describe euvolemic hyponatremia secondary to primary polydipsia.
Answer 3: These factors describe hypovolemic hyponatremia secondary to renal losses or mineralocorticoid deficiency.
Answer 4: These factors describe hypervolemic hyponatremia secondary to CHF, cirrhosis, or nephrosis.
Answer 5: These factors describe hypervolemic hyponatremia secondary to renal failure. Fractional excretion of sodium would be >1%.

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