Symptoms of Hyponatremia
Hyponatremia presents with symptoms ranging from mild and nonspecific (nausea, weakness, headache) to severe and life-threatening (seizures, coma, cardiorespiratory distress), with symptom severity depending on the rapidity of onset, duration, and degree of sodium reduction. 1, 2
Mild to Moderate Symptoms
Nonspecific manifestations that occur with mild hyponatremia (130-135 mEq/L) include:
- Nausea and vomiting 1, 2, 3
- Weakness and fatigue 1, 2
- Headache and dizziness 1, 3
- Muscle cramps 4
- Mild neurocognitive deficits including impaired concentration 1
- Gait instability 1
Chronic Mild Hyponatremia Complications
Even mild chronic hyponatremia (130-135 mEq/L) causes significant morbidity that is often underrecognized:
- Cognitive impairment and attention deficits 1, 5
- Increased fall risk (23.8% vs 16.4% in normonatremic patients) 1
- Higher fracture rates (23.3% vs 17.3% over 7.4 years) 1
- Secondary osteoporosis 1
- Increased hospital mortality (60-fold increase with sodium <130 mEq/L: 11.2% vs 0.19%) 5
Severe Symptoms Requiring Emergency Treatment
Severe symptomatic hyponatremia constitutes a medical emergency and includes:
- Seizures 1, 2, 3, 6
- Altered mental status: confusion, delirium, obtundation 1, 2, 3
- Impaired consciousness progressing to coma 1, 2, 6
- Ataxia and severe gait disturbances 2
- Cardiorespiratory distress 1
- Brain herniation and death (rare) 2, 6
Symptom Severity Determinants
Three critical factors determine symptom severity:
- Rapidity of onset: Acute hyponatremia (<48 hours) causes more severe symptoms than chronic 1, 5
- Degree of sodium reduction: Severe hyponatremia (<125 mEq/L) produces more pronounced symptoms 5, 2
- Duration: Chronic hyponatremia allows partial cerebral adaptation, reducing acute neurological symptoms but causing insidious complications 1, 5
Clinical Significance by Sodium Level
Hyponatremia severity classification guides symptom expectations:
- Mild (130-135 mEq/L): Minimal symptoms, but increased fall risk and mortality 5, 2
- Moderate (125-129 mEq/L): More pronounced weakness, nausea, cognitive changes 2, 6
- Severe (<125 mEq/L): High risk of seizures, coma, and life-threatening complications 5, 2
Common Pitfall
Ignoring mild hyponatremia (130-135 mEq/L) as clinically insignificant is a critical error, as this range is associated with substantial morbidity including falls, fractures, cognitive impairment, and increased mortality. 5, 1