Title: Severe Hyponatremia: A Case Study
Authors: Tianfu Shang, OMS I; Mark Baldwin DO, FACOI, FASN; Adam Ruscher MD, CM, FAAEM; Muniba Javed MD FABIM, FASN
Introduction
Hyponatremia is the most common electrolyte abnormality seen in clinical practice; severe hyponatremia is defined as serum sodium (Na) <120 mmol/L (n 135-145). This is especially common in the elderly where the effects of age and medication play key roles. Clinical presentation ranges from asymptomatic to life threatening neurological symptoms. The most significant factor is the time course of the decreased sodium level and the brain’s ability to make transcellular osmotic compensations. Generally, neurologic manifestation increases with the rate of change. A thorough and rapid assessment of volume status is essential for not only diagnosis but also to guide appropriate therapy. Treatment is based on judicious Na replacement titrated to a gradual increase by 4-8 mmol/L/day. Rapid correction increases the risk of osmotic demyelination syndrome (ODS) and irreversible brain injury.
Case Description
We describe a 66-year-old female who presented to the emergency department with a weeklong history of nausea, vomiting, diarrhea, poor intake, and lethargy. Her baseline sodium and creatinine (Cr) levels several months prior to admission were normal. She had been taking lisinopril, metoprolol, and sertraline as an outpatient. Initial labs revealed a Na of 92 mmol/L (n 135-145), Cr of 6.57 mg/dL (n 0.7-1.1), serum osmolarity was 230 mOsm/kg (n 270-280), and urine osmolarity of 216 mOsm/kg (n 500-850). She was given 2 liters of normal saline intravenously with repeat Na of 100 mmol/L. This exceeded the recommended rate of increase; nephrology was consulted, and the patient was given 1 mcg of desmopressin subcutaneously and the rate of Na correction reduced. Upon stabilization, she was transferred to the intensive care unit for continued Na correction and close observation. On hospital day 6, she experienced a period of decreased mentation without evidence of pontine demyelination on MRI. She was discharged on day 11 with a Na of 139 and Cr of 3.48.
Discussion
This case of severe hyponatremia was complicated by the patient’s prior medications, chronic volume depletion, and resultant acute kidney injury (AKI). While sertraline and lisinopril have well-recognized effects on renal function, the patient’s significant volume loss and rapid response to fluid replacement points towards hypotonic hyponatremia. A gradual correction of Na allowed for the patient to return home after only 11 days in the hospital. This case supports prior literature of a biphasic but safe sodium correction rate of 4-6 mmol/L/day for severe hyponatremia.
I am one of the judges on your case study. At the end, you described a few options of what could have been driving her hyponatremia, based on what you know about the case and the diagnosis, what do you think is the most likely cause for her presentation and why do you think that?
Thank you for your attention and interest, Dr. Callan. Given her past history, we believe this incidence of severe hyponatremia is most likely an acute presentation of hypovolemic hyponatremia, secondary to possible underlying SIADH from long-term sertaline use. While her prior labs, which were not recent, did not show chronic hyponatremia, the well documented prevalence of SIADH following chronic sertaline use leads us to believe her admission tangentially related to her sertaline use. This is compounded by her recent volume loss via GI upset with minimal fluid intake which caused AKI and further exacerbated her hyponatremia. Thank you for your inquiry.
Judge: What preventative actions would you suggest to help prevent a second occurrence of hyponatremia?
Thank you for your attention and interest, Dr. Novack. Preventative measures for this patient specifically were begun upon admission, this included discontinuation of any medications that exacerbate hyponatremia, volume maintenance, and improving kidney function. In general, hyponatremia is prevented by close monitoring of those at risk, i.e. the elderly, those on hyponatremic medications, and extreme athletes. Non-pharmaceutical preventative steps include education of individual risk factors, close medication adherence, and consistent volume repletion titrated to exercise intensity. Thank you for your inquiry.
Thank you for your presentation. After 11 days in the hospital with severe hyponatremia, how long would it take for the patient to resume “normal activities?”
Thank you for your attention and interest, Dr. Walser. Upon discharge the patient had full neurological function and all lab values were WNL. The patient was downgraded from ICU to the acute care unit on day 7. Upon transfer to the acute care unit plans were initiated for her eventual discharge including progressive ambulation trials, consultation with SLP, RD, and PT. The details of these consultations were not within the original scope of the case report and therefore were not requested as part of the patient file. Follow up visits with her PCP and nephrologist reported uneventful outpatient recovery without any deficits or sequelae reported. Thank you for your inquiry.