Question
A patient with small cell lung carcinoma has symptomatic hyponatraemia (serum sodium 127 mmol/ L). The most likely etiology is:
The correct answer is
Syndrome of inappropriate ADH
SCLC and Hyponatraemia Etiology
Small cell lung carcinoma (SCLC) is frequently associated with paraneoplastic syndromes. A common complication is the Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH).
Understanding SIADH in SCLC
SIADH causes the body to retain excessive water due to increased levels of antidiuretic hormone (ADH). This leads to dilution of the blood's sodium concentration, resulting in hyponatraemia.
- The patient's low serum sodium level is '$127 \text{ mmol/L}$', confirming hyponatraemia.
- SCLC is a known cause of ectopic ADH production, leading to SIADH.
- Symptomatic hyponatraemia is a typical presentation.
Evaluating Other Options
The other conditions are less likely causes of hyponatraemia in this specific clinical context:
- Fanconi Syndrome affects kidney tubules and doesn't typically present as the primary cause of hyponatraemia linked to SCLC.
- Cushing's Syndrome involves excess cortisol and is usually associated with normal or high sodium levels.
- Metabolic Syndrome is a group of risk factors for heart disease and diabetes and is not directly linked to causing hyponatraemia in SCLC patients.
Therefore, SIADH is the most probable cause.
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Important Questions from Electrolyte Imbalance
- Which of the following does NOT cause prolongation of QT interval?
- Which of the following does NOT causes polyuria?
- A 36-year old chronic alcoholic, malnourished male is hospitalized with pneumonia. His condition worsens after aggressive treatment with intravenous dextrose and antibiotics. This phenomenon of 'Refeeding Syndrome' is accompanied by which one of the following biochemical alterations?
- Which one of the following drugs causes hypercalcemia?
- Syndrome of Inappropriate ADH secretion (SIADH) is usually associated with:
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