If serum osmolality 300 musm/ivg & urine osmolaUty is 1200 mOsm/kg, what is the diagnosis.
Correct Answer: SIADH
Description: The syndrome of inappropriate antidiuretic hormone secretion (SIADH) involves the continued secretion or action of arginine vasopressin (AVP) despite normal or increased plasma volume. The resulting impairment of water secretion and consequent water retention produces the hyponatremia (ie, serum Na+ < 135 mmol/L) with concomitant hypo-osmolality (serum osmolality < 280 mOsm/kg) and high urine osmolality that are the hallmark of SIADH. The key to understanding the pathophysiology, signs, symptoms, and treatment of SIADH is the awareness that the hyponatremia results from an excess of water rather than a deficiency of sodium. Depending on the magnitude and rate of development, hyponatremia may or may not cause symptoms. The history should take into account the following considerations: In general, slowly progressive hyponatremia is associated with fewer symptoms than is a rapid drop of serum sodium to the same value Signs and symptoms of acute hyponatremia do not precisely correlate with the severity or the acuity of the hyponatremia Patients may have symptoms that suggest increased secretion of AVP, such as chronic pain, symptoms from central nervous system or pulmonary tumors or head injury, or drug use Sources of excessive fluid intake should be evaluated The chronicity of the condition should be considered Ref Harrison20th edition pg 288
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