A 45-year-old man comes to the emergency department after experiencing sudden-onset headache with brief loss of consciousness while working in his yard. CT scan of the brain reveals blood in the basal cistern from a ruptured intracranial aneurysm. The patient is hospitalized, and endovascular coiling of the aneurysm is performed. Over the next several days, his symptoms gradually improve but the patient develops worsening hyponatremia. Which of the following is the most likely cause of this patient's hyponatremia?

Question

A 45-year-old man comes to the emergency department after experiencing sudden-onset headache with brief loss of consciousness while working in his yard.  CT scan of the brain reveals blood in the basal cistern from a ruptured intracranial aneurysm.  The patient is hospitalized, and endovascular coiling of the aneurysm is performed.  Over the next several days, his symptoms gradually improve but the patient develops worsening hyponatremia.  Which of the following is the most likely cause of this patient's hyponatremia?

Quizplus · Accepted Answer

11ec160b_3acb_3521_9249_c554da2dcec2_MD0001_00 This patient likely has the syndrome of inappropriate antidiuretic hormone secretion (SIADH), the most common cause of hyponatremia following subarachnoid hemorrhage (SAH). Antidiuretic hormone (ADH) is normally released by the hypothalamus and posterior pituitary in response to elevated serum osmolality (eg, following water deprivation) or decreased arterial blood volume. ADH promotes renal water reabsorption, which leads to concentration of the urine, extracellular fluid volume expansion, and lowering of serum osmolality and serum sodium. Hypothalamic damage following SAH is thought to trigger excessive production of ADH, resulting in the classic SIADH features of hypotonicity (ie, low serum osmolarity), hyponatremia, and persistently concentrated urine (ie, high urine osmolality). In addition to SIADH, hyponatremia after SAH can also be due to cerebral salt wasting (caused by increased secretion of brain natriuretic peptide, which leads to urinary sodium losses) or acute cortisol deficiency (eg, from pituitary injury, leading to hypotension) (Choice E). In both conditions, decreased extracellular fluid volume causes a secondary increase in ADH and worsening hyponatremia. (Choice A) In primary polydipsia, defective central thirst regulation leads to excessive water intake and hyponatremia. ADH levels are low, rather than high. Primary polydipsia is typically seen with certain psychiatric conditions (eg, schizophrenia) or use of psychotropic medications. It is not commonly associated with SAH. (Choice B) Impaired renal concentrating ability is seen in diabetes insipidus (DI), which occurs either due to ADH resistance (in nephrogenic DI) or decreased ADH production (in central DI). DI may follow cerebral injury; however, it does not cause hyponatremia. Rather, DI results in a clinical picture opposite that of SIADH, featuring hypernatremia, increased serum osmolality, and dilute urine (ie, low urine osmolality). (Choice C) Inadequate dietary intake of sodium is a rare cause of hyponatremia primarily seen in cases of chronic alcohol abuse (eg, beer potomania). SIADH is a more likely cause of hyponatremia in this patient. Educational objective: Hyponatremia following cerebral injury (eg, subarachnoid hemorrhage) is commonly due to the syndrome of inappropriate antidiuretic hormone secretion. Injury to the hypothalamus leads to increased secretion of antidiuretic hormone, which in turn leads to water retention, low serum osmolality, and increased urinary sodium excretion. __________ References: Diagnosis and management of subarachnoid hemorrhage. (http://www.ncbi.nlm.nih.gov/pubmed/26426230) Hyponatremia after spontaneous aneurysmal subarachnoid hemorrhage - a prospective observational study. (http://www.ncbi.nlm.nih.gov/pubmed/31154098)

A 45-Year-Old Man Comes to the Emergency Department After Experiencing