Kidney Week

Abstract: PUB066

Chronic Hyponatremia: An Overlooked Contributor to Severe Osteoporosis (OP)

Session Information

• Publication Only

Category: Bone and Mineral Metabolism

• 502 Bone and Mineral Metabolism: Clinical

Authors

• Vega, Melissa Mia, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States

Melissa Mia Vega, MD

• Obeidat, Yasin, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States

Yasin Obeidat, MD

• Mansoor, Sobia, Landmark Medical Center, Woonsocket, Rhode Island, United States

Sobia Mansoor, MD

• Braden, Gregory Lee, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States

Gregory Lee Braden, MD

• Abdullin, Marat, University of Massachusetts Chan Medical School - Baystate Regional Campus, Springfield, Massachusetts, United States

Marat Abdullin, MD, PhD

Introduction

Mild chronic hyponatremia has been associated with increased bone fractures. Often attributed to alterations in gait and mental status, its direct effect on bone density is frequently overlooked. We describe a case of severe OP in the setting of chronic hyponatremia.

Case Description

A 54-year-old woman with history of migraines, partial hysterectomy and severe OP was evaluated due to chronic mild hyponatremia and hypercalciuria. Serum sodium (sNa) was 130-134 mmol/L over the past 5 years. Serum osmolality 274 mOsm/kg, urine osmolality 592 mOsm/kg, and uric acid was 2.4 mg/dL, pointing towards SIADH. Urine calcium was high over the past year: 254-554 mg/24h, PTH 31 pg/mL, Calcium 9.4 mg/dL. Physical exam was negative for blue sclerae or hearing loss. Vitamin D and TSH are within normal. Renal US is negative for stones and nephrocalcinosis. She was diagnosed with OP a year ago, T-score of –3.0 of AP spine. No history of pathologic fractures. Was on topiramate 100 mg daily for over 10 yrs but stopped 5 yrs ago. She exercises regularly, is vegan, takes calcium supplements and has high water intake. SPEP was unremarkable and age-appropriate cancer screenings were negative. History is negative for any other secondary cause of OP. Has been started on bisphosphonates. Recent sNa is 131 mmol/L. Fluid restriction and sodium tablets were started with continued monitoring until resolution of hyponatremia. Plan to repeat DXA scan in one year.

Discussion

OP is associated with high risk of morbidity, mortality and decreased quality of life. Animal studies have shown that hyponatremia leads to decreased bone density. Retrospective studies paint a clear association between the two. One third of total body sodium is stored in bones. The mobilization of sodium leads to increased bone resorption by direct activation of osteoclasts. Elevated ADH levels activate osteoclasts and downregulate osteoblasts. Hypercalciuria, which can be caused by SIADH, is another contributor to OP. This patient has severe OP despite adequate calcium intake and consistent exercise. Chronic hyponatremia due to SIADH represents a previously unrecognized contributor to her OP. We hope to see improvement in both her hypercalciuria and bone density with the resolution of her hyponatremia. This case highlights hyponatremia as a potentially overlooked and modifiable risk factor for OP.

Digital Object Identifier (DOI)

• doi: 10.1681/ASN.202564xfy4y9