Case Series: Hyponatremia Associated With Moderate Exercise

Abstract

Exercise-induced hyponatremia is commonly believed to be associated only with extraordinary physical efforts, or particularly strenuous exercise. Hyponatremia complicating moderate exercise has not been described previously. The authors describe the characteristics of seven patients with life-threatening hyponatremia associated with mild to moderate exercise. All patients suffered from nausea, vomiting, agitation, and confusion, appearing during or after moderate physical activity. Grand mal convulsions occurred in five of the patients. In laboratory results, hyponatremia was as low as 115 mEq/L, with a relatively high sodium concentration in the urine. High serum creatine kinase activity levels were found in most of the patients. All patients were discharged in good condition, without neurologic sequela. The authors conclude that hyponatremia is a possible complication of moderate exercise, and not only of endurance sports, and that exercise-induced hyponatremia can produce severe neurologic manifestations. The mechanism of the hyponatremia is unclear, but may be due to a hemodynamically inappropriate stimulus for antidiuretic hormone secretion.

Exercise-Associated Hyponatremia

“…Several studies have examined the incidence of hyponatremia in this cohort, and a range of 6 to 30% of these athletes had serum sodium values below normal (9,10,12,(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). The wide range of incidence likely reflects differences in fluid replacement guidelines that were prevalent at the time and place of the study.…”

“…However, recent studies have shown that endurance athletes not uncommonly develop hyponatremia at the end of the race, usually in the absence of clear central nervous system symptoms (9,10,12,(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). For example, in the 2002 Boston Marathon, Almond et al (15) found that 13% of 488 runners studied had hyponatremia (defined as a serum sodium concentration of 135 mmol/L or less) and 0.6% had critical hyponatremia (serum sodium concentration of 120 mmol/L or less).…”

Hiker Fatality From Severe Hyponatremia in Grand Canyon National Park

“…[1][2][3][4][5] The first documented EAH death was of a marathoner in 1993, 4 and EAH has also been identified as a potential problem among hikers for more than 2 decades. [6][7][8][9][10][11][12][13][14] As far as we are aware, the present report is the first documented fatal case of EAH in a hiker. We share this case because proper initial management of EAH can be critical to the outcome, and there is evidence that current treatment guidelines for EAH have yet to be universally adopted.…”

“…[27][28][29] Excessive losses of urine sodium due to secretion of brain natriuretic peptide may also contribute to the pathophysiology of EAH. 14,30,31 Early symptoms of EAH include nausea, vomiting and headache, which can rapidly progress to confusion, altered mental status, seizure, and death if untreated. 26 Often, there is a delay in the presentation of symptomatic EAH after exercise cessation.…”

“…Emergency medical practitioners should be aware of current management guidelines for EAH because the persistent common treatment with high volumes of isotonic fluids has been associated with delayed recovery, 5,9,13,14,16,17,20,22,24,32,34 and has likely contributed to deaths. 34,36 Conversely, early recognition and treatment of symptomatic EAH with hypertonic saline has been demonstrated to be safe and effective, and is now the mainstay of current management guidelines.…”