Journal of the American Society of Nephrology
Introduction: Small cell lung cancer (SCLC) is an aggressive neuroendocrine lung cancer associated with paraneoplastic syndromes – syndrome of inappropriate ADH (SIADH) in 7-16% of cases and Ectopic ACTH Syndrome (EAS) in 3.5-4.3% of cases. Both syndromes are associated with a poor prognosis in patients with SCLC. We describe a patient who presented with SIADH, leading to a diagnosis of SCLC who subsequently developed EAS. Case Description: A 71-year-old female with a past medical history of hypertension, depression, and tobacco use presented with lethargy. She noted headache, but otherwise was unable to provide history due to altered mentation. Per her family, the patient recently had pneumonia treated with antibiotics and steroids and was complicated by hyponatremia. Upon evaluation, our patient was hemodynamically stable, with labs revealing Na 106 mmol/l, K 3.9 mmol/l, Cl 74 mmol/l, BUN 6 mg/dl, and creatinine 0.52 mg/dl. Serum osmolality was 232 mOsmol/kg, urine osmolality 543 mOsmol/kg, urine Na 130 mmol/l and urine Chloride 128 mmol/l. TSH was within normal limits and random cortisol level was 63.4 mcg/dl. She was managed in ICU with a DDAVP clamp and 3% saline. She was discharged on Urea therapy, which was later change to furosemide and sodium chloride tablets due to cost. At discharge, the etiology of her hyponatremia was most consistent with SIADH. CT scan of the chest followed by PET scan showed multiple enlarged mediastinal lymph nodes that were considered suspicious for malignancy. Lymph node biopsy confirmed metastatic SCLC. Our patient was started on concurrent chemotherapy and radiotherapy. Upon follow up, progression of her cancer was seen, prompting additional chemotherapy with carboplatin, etoposide, and atezolizumab. She was admitted 11 months after her first presentation due to hypernatremia and hypokalemia. She had metabolic alkalosis with a bicarbonate of 36 mmol/l, Na level 146 mmol/l, and K 2.7 mmol/l. Morning cortisol level was 54.2 mcg/dl and ACTH was 63 pg/ml. Cortisol level after low dose dexamethasone suppression test remained elevated at 66.6 mcg/dl. In the setting of active SCLC, findings were most suggestive of ectopic ACTH secretion. Discussion: There are only 8 cases reported in literature with simultaneous or sequential EAS and SIADH. Cortisol and ADH have opposite effects on kidney sodium excretion. This may lead to masking of EAS by SIADH, leading to underdiagnosis.
Sardarli K, Morris AM, Abukhaled J. Dual paraneoplastic syndrome in small lung cancer. J Am Soc Nephrol. 2022;33(Abstact Suppl):736.