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Understanding Hyponatremia

Symptoms of Hyponatremia

Hyponatremia is more likely to be symptomatic when the decrease in serum sodium concentration is large and occurs rapidly.^1,2 It is important to recognize, however, that the clinical presentation of hyponatremia can be quite variable.¹

“Symptoms are related largely to dysfunction of the central nervous system and are more evident when the decrease in the serum sodium concentration is large or fast.”¹

—I Douglas. Cleve Clin J Med. 2006

Acute symptomatic—In acute symptomatic hyponatremia, serum sodium concentration falls rapidly (in less than 48 hours).¹

Chronic (symptomatic or asymptomatic)—Chronic hyponatremia is defined as hyponatremia lasting more than 48 hours or with an unknown duration.¹ In patients with chronic hyponatremia, treatment must be addressed cautiously because of adaptation by the brain to this prolonged state.^1,2 Chronic asymptomatic hyponatremia generally calls for a more conservative approach than chronic symptomatic hyponatremia.¹

Interestingly, although mild, chronic hyponatremia is often thought to be asymptomatic, a recent study found that it actually can be accompanied by impairments in both gait and attention.³ In a case-control study, Renneboog et al found that 21.3% of patients with chronic, asymptomatic hyponatremia were admitted to the ER with falls, compared with 5.3% of control patients—the authors hypothesized a link between falls and the impairments in gait and attention.³

In patients with severe hyponatremia (serum sodium <125 mEq/L), central nervous system symptoms predominate and can progress to seizures, coma, or death.¹ Other neurological symptoms include¹:

• Headache
• Muscle cramps
• Reversible ataxia
• Psychosis
• Lethargy
• Restlessness
• Disorientation
• Apathy
• Anorexia
• Agitation

Neurological symptoms are generally less common in patients with chronic or mild hyponatremia (serum sodium >125 mEq/L).¹

Nonneurological symptoms of hyponatremia include¹:

• Fatigue
• Thirst
• Weakness
• Cramping
• Nausea
• Vomiting
• Bloating
• Swelling
• Tightness of hands and feet

NEXT: Management of Dilutional Hyponatremia

References: 1. Douglas I. Hyponatremia: why it matters, how it presents, how we can manage it. Cleve Clin J Med. 2006;73(suppl 3):S4-S12. 2. Verbalis JG, Goldsmith SR, Greenberg A, Schrier RW, Sterns RH. Hyponatremia treatment guidelines 2007: expert panel recommendations. Am J Med. 2007;120(suppl 11A):S1-S21. 3. Renneboog B, Musch W, Vandemergel X, Manto MU, Decaux G. Mild chronic hyponatremia is associated with falls, unsteadiness, and attention deficits. Am J Med. 2006;119:71.e1-71.e8.