Symptoms of Hyponatremia
Hyponatremia symptoms range from mild and nonspecific to severe and life-threatening, including headache, nausea, vomiting, confusion, lethargy, muscle cramps, seizures, and coma, with severity depending on both the sodium level and rapidity of onset. 1
Classification of Hyponatremia
Hyponatremia is defined as a serum sodium concentration <135 mEq/L and is classified by severity:
- Mild: 126-135 mEq/L
- Moderate: 120-125 mEq/L
- Severe: <120 mEq/L 1
It's also categorized by timing:
- Acute: Developed within 48 hours
- Chronic: Developed over >48 hours 1
Symptom Progression Based on Severity
Mild Hyponatremia (130-134 mEq/L)
- Subtle cognitive impairment
- Gait disturbances
- Increased risk of falls and fractures
- Weakness
- Mild headache 2, 3
Moderate Hyponatremia (125-129 mEq/L)
Severe Hyponatremia (<125 mEq/L)
- Delirium
- Confusion
- Impaired consciousness
- Ataxia
- Seizures
- Coma
- Brain herniation (rare)
- Death (rare) 3
Acute vs. Chronic Symptoms
Acute hyponatremia (developing in <48 hours) typically produces more severe neurological symptoms at the same sodium level compared to chronic hyponatremia. This is because the brain has not had time to adapt to the osmotic changes 5, 1.
Special Considerations in Different Populations
Children
Children are at particularly high risk of developing symptomatic hyponatremia because of their larger brain-to-skull size ratio, which leaves less room for brain swelling 5.
Athletes
In endurance athletes, exercise-associated hyponatremia (EAH) may present with:
- Bloating
- Nausea and/or vomiting
- Headache
- Altered mental status
- Potential collapse
- Seizure
- Coma due to acute cerebral edema 5
Warning Signs of Hyponatremic Encephalopathy
Hyponatremic encephalopathy is a medical emergency that can be fatal or lead to irreversible brain injury if inadequately treated. Key warning signs include:
- Somnolence
- Obtundation
- Seizures
- Cardiorespiratory distress 2
Common Pitfalls in Recognizing Hyponatremia
Nonspecific early symptoms: Initial symptoms like headache, nausea, and fatigue can be mistaken for other conditions.
Delayed diagnosis: Symptoms of hyponatremia can be nonspecific, including fussiness, headache, nausea, vomiting, confusion, lethargy, and muscle cramps, making prompt diagnosis difficult 5.
Overlooking chronic mild hyponatremia: Even mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures 2.
Medication-induced hyponatremia: Many medications can cause hyponatremia, which may be clinically symptomatic or asymptomatic and is frequently underdiagnosed 6.
Failure to recognize the urgency of severe symptoms: Severely symptomatic hyponatremia with signs of somnolence, obtundation, coma, seizures, or cardiorespiratory distress is a medical emergency requiring immediate treatment 2.
By recognizing these symptoms early and understanding their progression, clinicians can intervene appropriately to prevent the potentially fatal complications of severe hyponatremia.