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SIADH — SCE Medical Oncology MCQ

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ModerateOncological EmergenciesSIADHSCE Medical Oncology

A 55-year-old woman presents to the acute oncology service with confusion and a serum sodium of 118 mmol/L. She has SCLC and is receiving chemotherapy. Serum osmolality is low (260 mOsm/kg), urine osmolality is inappropriately concentrated (450 mOsm/kg), and urine sodium is 45 mmol/L. She is euvolaemic. What is the diagnosis and initial management?

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Correct answer: B — SIADH — fluid restriction (750-1000 mL/day) and treat the underlying malignancy

SIADH is the most common paraneoplastic cause of hyponatraemia in SCLC (occurring in approximately 10-15% of SCLC patients). The diagnostic criteria include: euvolaemic hyponatraemia, low serum osmolality, inappropriately concentrated urine (>100 mOsm/kg), urine Na >30 mmol/L, normal thyroid and adrenal function. Initial management is fluid restriction (750-1000 mL/day). For severe/symptomatic cases, hypertonic saline (with care to avoid overcorrection — max 10 mmol/L per 24h). Demeclocycline or tolvaptan may be needed for refractory cases.

Reference: ESMO 2024 Oncological Emergencies Guidelines; NICE NG122 Lung cancer