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Question Date: 22/02/2024


Question: A 32-year-old man presents to the emergency room with weakness, numbness, and paresthesias in his distal lower extremities that have ascended over the course of 2 days to the level of his hips. His hands are also now symptomatic. On examination, he is also noted to have no reflexes in his arms or legs. There was no preceding infection. Spinal fluid analysis reveals cytoalbuminologic disassociation, and a diagnosis of Guillain-Barr syndrome (GBS) is made. Laboratory evaluation performed on presentation was also notable for hyponatremia. Which is most likely to explain his hyponatremia?


Options:

  • Cerebral salt wasting
  • Dehydration
  • Intravenous immunoglobulin (IVIG)
  • Syndrome of inappropriate antidiuretic hormonesecretion (SIADH)


Correct Answer: Syndrome of inappropriate antidiuretic hormonesecretion (SIADH)


Explaination: SIADH has been reported in Guillain-Barr syndrome (GBS), though the pathophysiology is not known. Among patients with GBS, SIADH is an independent risk factor for increased mortality, as areage >50, requirement of ventilator support, hyponatremia, and bulbar weakness. In SIADH, excessantidiuretic hormone (ADH) prevents water loss in the kidneys, leading to decreased serum osmolality andserum sodium concentration with elevated urine osmolality and urine sodium concentration. Other etiologies of hyponatremia include excessive water intake (psychogenic polydipsia), functional hypovolemia (congestive heart failure CHF and cirrhosis), and some cases of dehydration (hypovolemic hyponatremia). It is notable that patients with SIADH generally appear euvolemic, as opposed to cerebral salt wasting, where patients appear hypovolemic. Cerebral salt wasting is most often seen in brain injuries or central nervous system (CNS) tumors, and is associated with large urinary output due to inability to retain sodium in the body, and therefore high urinary excretion of sodium. Treatment for cerebral salt wasting is replacement of fluid andsodium, whereas treatment for SIADH is fluid restriction. The excess fluid given with IVIG can causepseudohyponatremia, but this patient has not received any treatment yet.


Reference: ( Bradleys NiCP, 7th edn, Chs. 52, pp. 696712 and 55, pp. 742-757).