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Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is characterized by excessive unsuppressible release of antidiuretic hormone (ADH) either from the posterior pituitary gland, or an abnormal non-pituitary source.
Ordinarily, ADH is a substance produced naturally in an area of the brain called the hypothalamus.
It is then released by the pituitary gland at the base of the brain.
ADH causes the body to retain water.
Common situations when ADH is released into the blood when it should not be produced (inappropriate) include:
Rare causes include:
Unsuppressed ADH causes an unrelenting increase in solute-free water being returned by the tubules of the kidney to the venous circulation.
A 74-year-old male patient recovering from a surgical procedure complains of headache, difficulty concentrating, impaired memory, muscle cramps, and weakness of 48 hours duration. On examination, vital signs are all within normal range, and there are no signs of dehydration or of edema. Laboratory values report serum sodium of 130 mmol/L. Which of the following would be compatible with a differential diagnosis of syndrome of inappropriate ADH secretion?
The correct answer is D.
This patient presents with low sodium levels and a differential diagnosis of syndrome of inappropriate antidiuretic hormone secretion (SIADH). SIADH is the excessive and inappropriate release of antidiuretic hormone despite a lack of physiologic signal (increased osmolarity or decreased blood volume). This person will have low volume of very concentrated urine.
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