WCN26-6956 RENAL BIOPSY IN MULTIPLE MYELOMA: AN OLD QUESTION WITH A NEW ANSWER; AN UPDATED ONCONEPHROLOGY MODEL

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.