Hyponatremia in a Small Cell Lung Cancer Patient: A Case Study

Orlando—Patients with small cell lung cancer may develop euvolemic hyponatremia due to low solute intake, syndrome of inappropriate antidiuretic hormone secretion (SIADH), or renal salt wasting from a platinum-based alkylating agent. Renal tubular injury, salt-magnesium and potassium-wasting have been associated with cisplatin; carboplatin, with a relatively lower nephrotoxic profile, is considered a safer alternative.

Omar Rabadi, MD, and colleagues presented a case study of a 67-year-old male with hyponatremia during a poster session at the NKF 2017 Spring Clinical Meetings in a poster titled Hyponatremia in a Patient with Small Cell Lung Cancer Caused by Carboplatin. The patient’s hyponatremia was diagnosed as he presented to the emergency department with tachypnea and sweating.

The patient was found to have a serum sodium level of 121 mmol/L. SIADH was suspected as the cause of the hyponatremia; further work up, including computerized tomography of the chest, revealed a lung mass, which was diagnosed as small cell lung cancer on biopsy. Cisplatin was avoided due to the concern of salt-wasting nephropathy; the patient was treated with carboplatin and etoposide.

Worsening hyponatremia led to readmission after a week (serum sodium level, 116 mmol/L) and orthostatic hypotension. Results of 24-hour urine study were: sodium level, 195 mmol/l; magnesium level, 207.5 mg/d; and potassium level, 149 mmol/d. Those results were indicative of renal sodium, potassium, and magnesium wasting. The patient was started on oral salt tables (8-10 g), potassium chloride (80 meq), and magnesium oxide (400 mmol) supplements daily.

Orthostatic hypotension, hypokalemia, and hypomagnesemia resolved and serum sodium improved to 121 mmol/L. Repeat 24-hour urine studies in the 2 weeks following continued to show evidence of electrolyte loss; however, serum sodium stabilized at 125 mmol/L.

“We report carboplatin induced tubulopathy that manifested as orthostatic hypotension, acute on chronic hyponatremia, hypokalemia, and hypomagnesemia. Ascertainment of correct etiology of hyponatremia is important in patients with cancer to guide appropriate management and follow-up. Twenty-four-hour urine collection may help us in correct diagnosis,” the researchers summarized.

Source: Rabadi O, Singh S, Karakala N, Jain N. Hyponatremia in a patient with small cell lung cancer caused by carboplatin. Abstract of a poster presented at the National Kidney Foundation 2017 Spring Clinical Meetings, April 19-22, 2017, Orlando, Florida.