How do you manage hyponatremia in a patient with Addison's disease?

Management of Hyponatremia in Addison's Disease

Hyponatremia in Addison's disease requires prompt treatment with both glucocorticoid and mineralocorticoid replacement therapy, along with isotonic saline administration for severe cases.

Pathophysiology of Hyponatremia in Addison's Disease

Hyponatremia in Addison's disease presents similarly to SIADH with:

• High urine sodium
• High urine osmolality
• Low serum osmolality
• Hypovolemia (unlike true SIADH)

This occurs due to:

1. Cortisol deficiency causing increased ADH release
2. Aldosterone deficiency leading to renal sodium wasting
3. Volume depletion further stimulating ADH release

Diagnostic Approach

When evaluating hyponatremia with suspected Addison's disease:

• Check morning serum cortisol (will be low)
• Measure ACTH (will be elevated)
• Assess plasma renin activity (will be increased)
• Measure aldosterone (will be low)
• Evaluate electrolytes (hyponatremia in 90% of cases) 1

Important clinical clues:

• Hyperpigmentation of skin and mucous membranes
• Hypotension, especially postural
• Weight loss, fatigue, anorexia
• Absence of hyperkalaemia does NOT rule out Addison's disease 2, 3

Treatment Algorithm

1. For Severe Hyponatremia with Adrenal Crisis:

• Immediate IV hydrocortisone: 100 mg bolus followed by 100-300 mg/day as continuous infusion or divided doses every 6 hours 1
• Aggressive fluid resuscitation: 3-4 L isotonic saline with initial rate of 1 L/hour 1
• Close monitoring: Frequent hemodynamic assessment and electrolyte measurements
• ICU admission for severe cases

2. For Chronic/Stable Hyponatremia:

• Glucocorticoid replacement: Hydrocortisone 15-25 mg daily in divided doses 1
• Mineralocorticoid replacement: Fludrocortisone 0.1 mg daily (range 0.05-0.2 mg) 4
• Salt supplementation if needed

3. Maintenance Therapy:

• Regular glucocorticoid replacement: Typically hydrocortisone 15-25 mg daily in divided doses
• Regular mineralocorticoid replacement: Fludrocortisone 0.1 mg daily 4
• Adjust doses based on clinical response and electrolyte normalization

Monitoring and Follow-up

• Monitor serum sodium and potassium regularly
• Assess blood pressure (postural hypotension suggests insufficient mineralocorticoid)
• Annual screening for other autoimmune conditions 1
• Educate patient on stress dosing and adrenal crisis prevention

Common Pitfalls to Avoid

1. Misdiagnosing as SIADH: Addison's hyponatremia can mimic SIADH with high urine sodium and osmolality 2
2. Waiting for hyperkalaemia: Not all Addison's patients present with elevated potassium 2, 3
3. Inadequate mineralocorticoid replacement: Fludrocortisone is essential for sodium retention
4. Overlooking stress dosing: Patients need increased glucocorticoid doses during illness or stress
5. Delayed treatment: Adrenal crisis requires immediate treatment without waiting for confirmatory tests 1

Special Considerations

• Rapid correction of severe hyponatremia can lead to osmotic demyelination syndrome
• Cerebral edema can occur in severe hyponatremia 5
• Patients with Addison's disease require lifelong hormone replacement and follow-up 6
• Annual screening for associated autoimmune conditions is essential 1