A 56-year-old man is brought to the emergency department due to progressive weakness and lethargy. The patient has also had a nonproductive cough for the past several weeks. He has no prior medical conditions and takes no medications. He has smoked a pack of cigarettes daily for 30 years. Physical examination shows no abnormalities. Chest x-ray reveals a lung mass. Further evaluation reveals an electrolyte abnormality induced by ectopic antidiuretic hormone production from a lung mass. This patient is at greatest risk of which of the following conditions if his electrolyte abnormality is corrected too quickly?

Question

A 56-year-old man is brought to the emergency department due to progressive weakness and lethargy.  The patient has also had a nonproductive cough for the past several weeks.  He has no prior medical conditions and takes no medications.  He has smoked a pack of cigarettes daily for 30 years.  Physical examination shows no abnormalities.  Chest x-ray reveals a lung mass.  Further evaluation reveals an electrolyte abnormality induced by ectopic antidiuretic hormone production from a lung mass.  This patient is at greatest risk of which of the following conditions if his electrolyte abnormality is corrected too quickly?

Quizplus · Accepted Answer

This patient's ectopic antidiuretic hormone production is likely to cause chronic hyponatremia due to excessive resorption of free water by the kidneys. Decreased serum tonicity causes water to cross the blood brain barrier and enter the central nervous system. In response to cellular swelling, brain cells excrete osmolytes (organic solutes [glutamate, myoinositol], electrolytes), resulting in intracellular water loss and normalization of brain volume. Overly rapid correction of chronic hyponatremia can cause osmotic demyelination syndrome (also known as central pontine myelinolysis). A rapid increase in extracellular tonicity (eg, due to aggressive saline hydration) quickly draws water out of central nervous system cells. The resulting uncontrolled cell shrinkage leads to degeneration of astrocytes (crucial for myelin maintenance) and oligodendrocytes. Demyelination typically affects the pons, but can also occur at extrapontine sites (eg, basal ganglia and cerebral white matter). Clinical features typically become apparent within 2-6 days. Features may include spastic quadriplegia (corticospinal tract involvement) and pseudobulbar palsy (dysphagia, dysarthria, tongue paresis). Patients with involvement of the bilateral pons may develop locked in syndrome with near-total paralysis and aphasia but with intact cognitive abilities, blinking, and vertical eye movements. (Choice A) Parathyroid hormone-related protein production is associated with squamous cell carcinoma of the lung; the resultant hypercalcemia can cause cardiac arrhythmias. However, rapid correction of hypercalcemia is not associated with arrhythmias. (Choice C) Cerebral edema results from rapid correction of hypernatremia with hypotonic fluids (free water flows into brain cells). This typically occurs in patients with chronic dehydration or diabetes insipidus (antidiuretic hormone deficiency or resistance), not with excessive antidiuretic hormone production. (Choices D and E) Severe hypophosphatemia can occur when feeding a severely malnourished patient (refeeding syndrome). It results in ATP depletion, which can cause hemolysis and rhabdomyolysis (diffuse myonecrosis). Patients require rapid correction of the phosphorus deficiency to prevent these conditions (unlike sodium, which should be corrected slowly to prevent osmotic demyelination). Educational objective: Rapid correction of chronic hyponatremia may lead to osmotic demyelination syndrome (also known as central pontine myelinolysis). It typically manifests 2-6 days after the osmotic insult with spastic quadriplegia, pseudobulbar palsy, and locked-in syndrome.

A 56-Year-Old Man Is Brought to the Emergency Department Due