Category: Adrenal Disorders
Objective : We report a patient with recurrent hyponatremia previously attributed to malignancy-associated syndrome of inappropriate antidiuretic hormone (SIADH) that revealed itself upon completion of chemotherapy, which included steroids, and who was ultimately found to have secondary adrenal insufficiency (AI).
Methods : NA
Results : A 58-year-old man with a history of type 2 diabetes mellitus, follicular B-cell lymphoma and a 42-pack-year history was referred to endocrine clinic for hyponatremia and subclinical hypothyroidism. Routine blood work obtained two years prior to consultation revealed a sodium of 120 mEq/L (135-145). The patient had no complaints and appeared euvolemic. Additional tests included potassium 4.2 mEq/L (3.5-5), serum osmolarity 253 mOsm/kg (278-305), urine osmolarity 821 mOsm/kg (500-800) and urine sodium 187 mmol/L (40-22). A diagnosis of SIADH was made and the patient was advised to restrict fluid intake. Repeat sodium level improved to 132 mEq/L. Due to prolonged tobacco use, a low-dose CT Chest was obtained and a work-up confirmed follicular B-cell lymphoma. Over the next 18 months the patient was treated with a regimen of bendamustine/rituximab and dexamethasone and his sodium levels normalized. After completion of chemotherapy, he was referred to endocrine for recurrent hyponatremia (125 mEq/L) and subclinical hypothyroidism (TSH 7 mmol/L (0.43-3.8), Ft4 0.86 ng/dL (0.71-1.85)). He was asymptomatic and euvolemic. Additional labs showed a low serum osmolarity relative to the urine and a morning cortisol of 4.79 mcg/dL (6-28) repeated and confirmed with an ACTH 33.9 pg/mL (7.2-63.3) and DHEA-S 21.4 ug/dL (49-344). Additional labs included negative thyroid antibodies, an appropriate 250 ug cosyntropin stimulation and completion of the pituitary panel, notable for low IGF-1 44 ng/mL (54-194). MRI pituitary showed likely macroadenoma with partial empty sella. The patient was started on hydrocortisone replacement with normalization of sodium, serum osmolarity, TSH and IGF-1 levels.
Discussion : Guidelines for the work-up and management of hyponatremia have been published with SIADH listed as a diagnosis of exclusion. Secondary AI may present like SIADH as cortisol deficiency induces an inappropriate increase in ADH resulting in hyponatremia. Our patient presented with euvolemic hyponatremia thought to be SIADH due to lymphoma which normalized with dexamethasone only to be “unmasked” once the treatment was completed. Patient’s TSH and IGF-1 also normalized, the former likely due to chronic AI, the latter due to mild elevation in TSH. This case highlights the importance for a comprehensive work-up before attributing euvolemic hyponatremia to SIADH.
Conclusion : NA.
Mount Sinai Hospital
New York, New York
Emily is an Endocrine fellow at Icahn School of Medicine at Mount Sinai.