Symptoms of Hyponatremia
Hyponatremia symptoms range from mild and nonspecific to severe and life-threatening, with severity depending on the rapidity of onset, duration, and degree of sodium reduction. 1
Mild Hyponatremia (130-134 mmol/L)
Mild hyponatremia often presents with subtle but clinically significant symptoms:
- Nausea and vomiting 2
- Weakness and fatigue 2
- Headache 2
- Mild neurocognitive deficits including lack of concentration and forgetfulness 3
- Apathy and loss of balance 3
Even mild chronic hyponatremia is associated with serious complications including cognitive impairment, gait disturbances, increased fall risk (23.8% vs 16.4% in normonatremic patients), and higher fracture rates (23.3% vs 17.3% over 7.4 years). 1 Hyponatremia is a secondary cause of osteoporosis. 1
Moderate Hyponatremia (125-129 mmol/L)
Moderate hyponatremia presents with more pronounced symptoms:
- More severe nausea and vomiting 4
- Confusion and disorientation 4
- Gait instability 4
- Increased fall risk (21% of hyponatremic patients present with falls compared to 5% of normonatremic patients) 4
Severe Hyponatremia (<125 mmol/L, especially <120 mmol/L)
Severe hyponatremia constitutes a medical emergency with life-threatening manifestations:
- Delirium and severe confusion 2
- Impaired consciousness progressing to somnolence and obtundation 1
- Ataxia 2
- Seizures (grand mal seizures possible) 3
- Coma 1, 3
- Cardiorespiratory distress 1
- Rarely, brain herniation and death 2
Critical Distinction: Acute vs. Chronic Onset
The rapidity of hyponatremia development dramatically affects symptom severity:
- Acute hyponatremia (<48 hours) causes more severe symptoms at any given sodium level compared to chronic hyponatremia 3
- Chronic hyponatremia (>48 hours) may be better tolerated, with patients sometimes remaining relatively asymptomatic even at sodium levels of 120-125 mmol/L 4
Clinical Significance and Mortality
Hyponatremia is associated with a 60-fold increase in hospital mortality (11.2% vs 0.19% in normonatremic patients) when sodium levels drop below 130 mmol/L. 4 Even mild hyponatremia is associated with increased hospital stay and mortality. 1
Common Pitfall to Avoid
Never dismiss mild hyponatremia (130-135 mmol/L) as clinically insignificant—this is a common error. 4 Even at these levels, patients experience increased mortality, fall risk, and cognitive impairment that warrant evaluation and appropriate management. 4, 1