Endocrine Abstracts

Introduction: Euvolemic hyponatremia (HN) caused by the Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) can predate a diagnosis of malignancy. It is thus essential to accurately diagnose the etiology of HN/SIADH when detected.

Methods: Retrospective, descriptive study of all 52 oncological/hematological malignancy patients diagnosed with SIADH in our Department between January 2011 and December 2016. HN was detected via computerized Primary-care/hospital case histories, and the computerized laboratory data base. Hyponatremia was considered to predate detection of malignancy/initiation of diagnostic study when a serum sodium (SNa) <135 mmol/l was detected 6 months before definitive oncological/hematological diagnosis (PTD). A patient was considered probably euvolemic (PE) when SNa descent was accompanied by a predominant pattern of lowering serum urea, creatinine and Uric acid levels, probably hypovolemic (PH) if urea, creatinine and Uric acid levels rose while not hypervolemic. SNa in mmol/l.

Results: Males: 32/52(61.5%), mean age:63.4 (S.D.:11)years. Etiology of SIADH: lung cancer: 18/52(34.6%), gastrointestinal: 6/52 (23.1%), genitourinary: 11/52 (21%), hematological: 5/52 (9.6%). 11/52 (21%) patients presented HN> 6 months PTD: median 40 (24–60), median age: 67 (63–76) years, initial SNa: 133 (130–134). Three patients were PH. Eight were PE, one receiving enalapril, another carbamazepine, another thiazide. In 5/8 (62%) PE patients, case histories revealed no initial cause for HN. HN was present a median of 25 (19–40.5) months PTD, range: 14–41. Initial SNa: 133 (129.5–133). None presented a low Urine Density. Hyponatremia was persistent, present in 42/50 (84%) tests, with a continuum up to ectopic-SIADH diagnosis, suggesting that SIADH induced their sustained hyponatremia. Etiology: lung (epidermoid), endometrial, breast, gastric, prostate. In only 1/11 (9%) patients was hyponatremia studied PTD, with SIADH workup responsible for prostate tumor diagnosis.

Conclusion: Mild hyponatremia can predate the diagnosis of a malignancy. However, in our series of 11/52 patients, in only one was hyponatremia studied. The lack of importance given to the finding of frank hyponatremia, albeit mild, could delay tumor diagnosis.