ASN's Mission

To create a world without kidney diseases, the ASN Alliance for Kidney Health elevates care by educating and informing, driving breakthroughs and innovation, and advocating for policies that create transformative changes in kidney medicine throughout the world.

learn more

Contact ASN

1401 H St, NW, Ste 900, Washington, DC 20005


The Latest on X

Kidney Week

Please note that you are viewing an archived section from 2022 and some content may be unavailable. To unlock all content for 2022, please visit the archives.

Abstract: SA-PO467

Syndrome of Inappropriate Antidiuresis (SIAD): A Clue to a Rare Diagnosis

Session Information

Category: Fluid‚ Electrolyte‚ and Acid-Base Disorders

  • 1002 Fluid‚ Electrolyte‚ and Acid-Base Disorders: Clinical


  • Sarwal, Amara, University of Utah Health, Salt Lake City, Utah, United States
  • Gilligan, Sarah, University of Utah Health, Salt Lake City, Utah, United States
  • Ramkumar, Nirupama, University of Utah Health, Salt Lake City, Utah, United States
  • Abraham, Josephine, University of Utah Health, Salt Lake City, Utah, United States

Syndrome of inappropriate antidiuresis (SIAD) was first described by Schwartz and Bartter in 1967. Small cell lung cancer is the malignancy most often associated with ectopic ADH release, however extrapulmonary small cell cancers, medications and other pulmonary disease can also be associated with SIAD. SIAD is rarely associated with prostate cancer. We report a case of SIAD with small cell carcinoma of the prostate.

Case Description

A 74-year-old man with history of cardiomyopathy, hypertension and left renal cancer with partial nephrectomy presented to our facility due to an irregular heartbeat. Upon further questioning, it was discovered that he had a 2 month history of gait unsteadiness, confusion and fatigue. He denied increased thirst or recent medication changes. He denied use of NSAIDs, PPIs, diuretics, SSRIs, or anti-epileptic medications. He is a former smoker with a 40 pack year history and is a social drinker. During initial workup in the emergency room, a sodium level of 125 mmol/L was discovered.

He was initially treated with furosemide and 4 gram salt tabs daily however eventually transferred to the critical care unit for hypertonic saline when his sodium dropped to 115 mmol/L within 72 hours. Further workup revealed a TSH of 1.25 mU/L, morning cortisol of 19 ug/dL, serum osmolality of 236 mOsm/kg with urine osmolality of 500 mOsm/kg and urinary sodium level of 155 mmol/L. MRI brain and CT chest were unrevealing, however his CT abdomen revealed an enlarged prostate with a heterogeneously enhancing large nodule and an enlarged right pelvic lymph node, concerning for metastatic prostate cancer despite a normal prostate specific antigen (PSA) at 0.5 ng/mL. Biopsy revealed small cell carcinoma of the prostate. Radiotherapy as well as chemotherapy with cisplatin and etoposide was initiated. He continued treatment with salt tablets and furosemide with stabilization of his sodium at 130-136 mmol/L.


Small cell carcinoma of the prostate is rare and accounts for <1% of all patients afflicted with prostate cancer. It is usually diagnosed at an advanced stage and PSA can be disproportionately low compared to conventional adenocarcinoma of the prostate. This case illustrates the need for diligent investigation when patients present with hyponatremia and SIAD.