The Question
A 19-year-old male who
recently returned from trekking in the Himalayas has had watery diarrhea for
one week. On examination he appears tired and mucous membranes are dry. BP is
105/70 and HR 80 sitting, BP 95/60 and HR 102 standing.
Laboratory Studies
Serum sodium 128 mEq/L
Serum potassium 2.8 mEq/L
Serum chloride 102 mEq/L
Serum bicarbonate 18 mEq/L
Blood urea nitrogen 48 mg/dL
Serum creatinine 1.1 mg/dL
Urine sodium <5 mEq/L
Urine osmolality 350 mOsm/kg
Which of the following would be the most appropriate management
of this patient:
A. Hypertonic saline
B. Demeclocycline
C. 0.9% NaCl and hydrocortisone
D. 0.9% NaCl and furosemide
E. 0.9% NaCl and KCl
The answer to the question of February 28, 2012 is D.
A 48-year-old male smoker presents with confusion and drowsiness. His only medications are bronchodilator and steroid inhalers. On examination, his BP is 130/84, HR 70, moist mucous membranes, good skin turgor, jugular venous pressure 4 cm, lung fields clear to auscultation, no peripheral edema. Chest radiograph shows emphysematous changes but is otherwise normal.
Laboratory Studies
Serum sodium 117 mEq/L
Serum potassium 3.6 mEq/L
Serum osmolality 258 mOsm/kg
Urine sodium 90 mEq/L
Urine potassium 75 mEq/L
Urine osmolality 662 mOsm/kg
Which of the following would be appropriate to identify the cause of hyponatremia in this patient:
A. Thyroid radioiodine scan
B. Cosyntropin stimulation test
C. Water deprivation test
D. Computed tomography scan of the chest
E. Psychiatry consult
Explanation
This is a case of euvolemic hyponatremia. The inappropriately high urine osmolality (>100 mOsm/kg) excludes primary polydipsia. Thus, the differential diagnosis is the syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypothyroidism, and hypoadrenalism. In this case, one should have a high index of suspicion for SIADH due to a bronchogenic carcinoma, and a chest CT is mandatory. Screening with a serum TSH is appropriate, but a thyroid scan is not indicated. The normotension, normokalemia and high urine potassium concentration make adrenal insufficiency unlikely.
(Source: Dr. Alan Yu, University of Kansas)
(Source: Dr. Alan Yu, University of Kansas)
