Hyponatremia - Signs and Symptoms

Signs and Symptoms

Symptoms of hyponatremia include nausea and vomiting, headache, confusion, lethargy, fatigue, appetite loss, restlessness and irritability, muscle weakness, spasms, or cramps, seizures, and decreased consciousness or coma. The presence and severity of symptoms are associated with the level of serum sodium, with the lowest levels of serum sodium associated with the more prominent and serious symptoms. However, emerging data suggest that mild hyponatremia (serum sodium levels at 131 mEq/L or above) is associated with numerous complications and undiagnosed symptoms.

Many medical illnesses, such as congestive heart failure, liver failure, renal failure, or pneumonia may be associated with hyponatremia. These patients frequently present because of primary disease symptomatology and are diagnosed after presenting due to manifestations of other medical issues.

Neurological symptoms often show for extremely low levels of sodium. When sodium levels in blood become too low, excess water enters cells and causes the cells to swell. Swelling in the brain is especially dangerous because the brain is confined by the skull and is unable to expand. The disorder in the brain caused by hyponatremia is called hyponatremic encephalopathy, and accounts for symptoms such as headache, nausea, vomiting and confusion, but can also present with seizures, respiratory arrest and non-cardiogenic pulmonary edema. Neurological symptoms most often are due to very low serum sodium levels (usually <115 mEq/L), resulting in intracerebral osmotic fluid shifts and brain edema. This neurological symptom complex can lead to tentorial herniation with subsequent brain stem compression and respiratory arrest, resulting in death in the most severe cases. The severity of neurological symptoms correlates with the rapidity and severity of the drop in serum sodium. A gradual drop, even to very low levels, may be tolerated well if it occurs over several days or weeks, because of neuronal adaptation. The presence of underlying neurological disease, like a seizure disorder, or non-neurological metabolic abnormalities, also affects the severity of neurologic symptoms.