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Secondary hyponatremia to inappropiate secretion of antidiuretic hormone Siadh in diagnosed patient of bladder cancer in treatment with chemotherapy: exclusion diagnosis?

Losada Vila Beatriz*, Carmen Pantin Gonzalez, Beatriz Anton Pascual, Nadia Sanchez Banos4, David Gutierrez Abad

This is a 65-year-old patient diagnosed in January 2018 of an epidermoid bladder carcinoma with bone involvement (extensive) with pain secondary to lumbar involvement, which starts treatment with antialgic radiotherapy followed by chemotherapy (Cisplatin+Gemcitabine) with palliative aim. However, after the first cycle of chemotherapy, his general state deteriorated, with hallucinations and somnolence, which is why his Primary Care Physician attributes the dose of morphine (110 mg/12 hours) and pregabalin that had been prescribed by intense pain. Descends dose up to 70 mg and suspends pregabalin but continues with drowsiness, so he goes to the Emergency Department. Analytical is performed showing Creatinine of 2.5 mg/dL (0.4-1.2), Potasium 7.2 mmol/L (3.5-5.1), Sodium 117 mmol/L (135-145), pH 7.23 (7.32-7.43), Bicarbonate 18 mmHg (22-29). Given that the patient was dehydrated, correction was initiated with fluid therapy (Saline 0.9%) and antihyperkalemia measures (salbutamol, resincalcium) with control in 6 hours that objective improvement of renal function to Creatinine 2.05 mg/dL, Potassium 6 mmol/L, Sodium 119 mmol/L, stable pH in 7.24 and bicarbonate 16 mmHg. Initially, therefore, improvement of renal function was seen but persistence of hyponatremia and metabolic acidosis. Urine ions are requested: urinary sodium 51 mmol/L, urine osmolality 574 mOsm/kg, and plasma osmolarity 210 mOsm/kg, compatible with SIADH. We added tolvaptan 30 mg daily with progressive improvement, so it is suspended after 3 weeks after restarting chemotherapy again.