What question did this study set out to answer?

To explore the relationship between electrolyte changes and dual paraneoplastic syndromes in small cell lung cancer (SCLC).

March 28, 2026Open Access

Wcn26-6956 Renal Biopsy in Multiple Myeloma: An Old Question With a New Answer; An Updated Onconephrology Model

Key Points

To explore the relationship between electrolyte changes and dual paraneoplastic syndromes in small cell lung cancer (SCLC).
Conducted urine and serum studies to analyze electrolyte levels.
Performed CT scans to assess adrenal and lung abnormalities.
Used dexamethasone suppression test to confirm ectopic Cushing syndrome.
Monitored patient’s electrolyte levels during treatment.
Patient developed triphasic electrolyte changes: initial hyponatremia, normalization during hypercortisolism, and recurrent hyponatremia.
CT scans revealed bilateral adrenal thickening associated with SCLC.
High cortisol levels showed mineralocorticoid activity complicating fluid balance.

Abstract

levels.CT scan revealed multiple lung and liver nodules, suggestive of disease recurrence.Instead, liver biopsy confirmed small cell lung cancer, for which chemotherapy/immunotherapy was initiated.Results: Nine months later, she presented with severe hypokalemia (2.3 mmol/L) and alkalosis (CO2 38 mmol/L) but was normonatremic (141) despite not taking her salt tablets.Urine studies revealed renal potassium wasting, and serum studies showed elevated AM cortisol (49.1 mcg/dL) and high ACTH (181 pg/mL).CT scan showed bilateral adrenal thickening.A high-dose dexamethasone suppression test confirmed ectopic Cushing syndrome, so she was started on metyrapone.Within 48 hours, her sodium declined from 138 to 130 mmol/L.Copeptin later came back at >5,000 pmol/L.Tolvaptan was considered, but fluid restriction, salt tablets, and urea normalized her sodium.Conclusion: Hyponatremia resolving to hypokalemia/alkalosis and recurring to hyponatremia again should raise the suspicion for dual paraneoplastic syndrome in SCLC.Our patient exhibited a triphasic electrolyte evolution, highlighting an intricate hormonal interplay: hyponatremia due to SIADH, normalization during hypercortisolism, and recurrent hyponatremia after cortisol reduction.The high cortisol's mineralocorticoid activity, overwhelming 11beta-hydroxysteroid dehydrogenase, likely masked hyponatremia, and then metyraponeinduced cortisol suppression may have unmasked a persistent ADHdriven water retention.Anticipating this triphasic course is key to the diagnosis and treatment of a rare dual paraneoplastic syndrome in SCLC.I have no potential conflict of interest to disclose.I did not use generative AI and AI-assisted technologies in the writing process.

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