What causes mild hyponatremia in adults?

Causes of Mild Hyponatremia in Adults

Mild hyponatremia (serum sodium 130-135 mEq/L) in adults is most commonly caused by medications, excessive alcohol consumption, very low-salt diets, and excessive free water intake, with management depending on the underlying volume status of the patient. 1

Classification of Hyponatremia

Hyponatremia is classified based on:

1. Severity:

   • Mild: 130-135 mEq/L
   • Moderate: 125-129 mEq/L
   • Severe: <125 mEq/L 2, 1

2. Volume status:

   • Hypovolemic
   • Euvolemic
   • Hypervolemic 2

Common Causes Based on Volume Status

Hypovolemic Hyponatremia

• Gastrointestinal losses: Vomiting, diarrhea 3
• Renal losses: Diuretic therapy (especially thiazides) 4
• Skin losses: Severe burns, excessive sweating 3
• Third-space losses: Pancreatitis, severe burns 3
• Low sodium intake: Very low-salt diets 1

Euvolemic Hyponatremia

• Medications: Antidepressants, antipsychotics, anticonvulsants, proton pump inhibitors 4
• Syndrome of Inappropriate ADH secretion (SIADH):
  • Malignancies (especially lung cancer)
  • CNS disorders
  • Pulmonary diseases
  • Pain
  • Nausea 5, 3
• Endocrine disorders:
  • Hypothyroidism
  • Adrenal insufficiency 3
• Reset osmostat syndrome 3
• Excessive water intake during exercise 1
• Psychogenic polydipsia 6

Hypervolemic Hyponatremia

• Cirrhosis: Chronic hyponatremia is common in patients with cirrhosis and ascites 7
• Heart failure: Activation of renin-angiotensin-aldosterone system 5
• Kidney disease: Nephrotic syndrome, advanced renal failure 3

Medication-Induced Hyponatremia

Medications are a frequent cause of mild hyponatremia 4:

• Diuretics: Especially thiazides, which impair urinary dilution
• Psychotropic drugs:
  • SSRIs (e.g., sertraline)
  • SNRIs
  • Antipsychotics
• Anticonvulsants: Carbamazepine, oxcarbazepine
• Other medications:
  • Proton pump inhibitors
  • Antibiotics
  • ACE inhibitors
  • Hypoglycemic agents
  • Amiodarone
  • NSAIDs 4

Alcohol-Related Hyponatremia

• Excessive alcohol consumption is a common cause 1
• Beer potomania syndrome (excessive beer intake with poor nutritional status)
• Alcohol can directly stimulate ADH release

Clinical Pearls and Pitfalls

• Even mild hyponatremia matters: Associated with cognitive impairment, gait disturbances, increased falls and fractures 5
• Check medication list: Meticulous history taking and recording of pharmacotherapy is essential to identify culprit medications 4
• Cirrhosis consideration: In patients with cirrhosis, chronic hyponatremia is common and usually not severely symptomatic until sodium levels drop below 110 mmol/L 7
• Diagnostic approach: Measuring plasma osmolality helps differentiate true hyponatremia from pseudohyponatremia or hyperglycemia-induced hyponatremia 3
• Urinary sodium measurement: Helps differentiate between renal and extrarenal causes of hyponatremia 3

Special Considerations

• In patients with cirrhosis and ascites, nearly half (49%) have hyponatremia (≤135 mEq/L) 7
• Patients with serum Na ≤130 mEq/L have increased risk of hepatic encephalopathy, hepatorenal syndrome, and spontaneous bacterial peritonitis 2
• Hyponatremia in cirrhosis reflects worsening hemodynamic status 2
• Rapid correction of chronic hyponatremia can lead to osmotic demyelination syndrome, a potentially devastating neurological condition 5

Remember that identifying the underlying cause of hyponatremia is essential for appropriate management, as treatment approaches differ based on volume status and etiology.