What are the symptoms and treatment for severe hyponatremia in a patient with Addison's disease, taking furosemide (Lasix), and inadequate mineralocorticoid replacement with fludrocortisone?

Symptoms of Severe Hyponatremia

Severe hyponatremia presents with neurological symptoms ranging from confusion and lethargy to seizures and coma, along with cardiovascular manifestations including hypotension and shock. 1

Neurological Manifestations

Severe hyponatremia causes progressive neurological deterioration that requires immediate recognition:

• Altered mental status progressing from non-specific malaise and somnolence to obtundation, confusion, and potentially coma if treatment is delayed 1
• Seizures represent a medical emergency requiring immediate hypertonic saline administration 1
• Impaired cognitive function with attention deficits even in milder cases 1
• Loss of consciousness in severe cases 1

The severity of neurological symptoms depends critically on both the absolute sodium level and the rapidity of decline. 2

Cardiovascular and Hemodynamic Features

In the context of Addison's disease with inadequate mineralocorticoid replacement, cardiovascular manifestations are particularly prominent:

• Hypotension (often severe) and shock are common manifestations 1
• Postural hypotension reflects insufficient mineralocorticoid therapy and/or low salt intake 3
• Dehydration is a key feature, caused by sodium wasting in urine 1
• Volume depletion leading to prerenal azotemia and decreased eGFR 3

Gastrointestinal Symptoms

• Nausea and vomiting (often severe) 1
• Abdominal pain 1
• Inability to tolerate oral intake, which creates a vicious cycle as patients cannot absorb their oral medications when they need them most 1

Musculoskeletal Manifestations

• Muscle pain and cramps 1
• Generalized weakness and fatigue 1

Laboratory Findings in Severe Hyponatremia with Addison's Disease

The laboratory profile helps distinguish this from other causes of hyponatremia:

• Hyponatremia is present in approximately 90% of newly presenting cases of primary adrenal insufficiency 4
• Hyperkalemia occurs in approximately 50% of patients at diagnosis, though its absence does not exclude Addison's disease 4, 5
• Increased creatinine and BUN due to prerenal renal failure from volume depletion 1
• Hypoglycemia more common in children but can occur in adults 4
• Metabolic acidosis due to impaired renal function and aldosterone deficiency 1
• Serum cortisol below normal range with markedly elevated plasma ACTH 4

Critical Clinical Pitfall

The classical combination of hyponatremia and hyperkalemia are not reliable markers for diagnosis because serum sodium is often only marginally reduced, whilst serum potassium is increased in only approximately one-half of patients at diagnosis. 4 In the presence of severe vomiting, hypokalemia and alkalosis may actually be present. 4

Specific Context: Addison's Disease with Inadequate Fludrocortisone

In your patient scenario with Addison's disease taking furosemide and inadequate fludrocortisone replacement:

• Chronic under-replacement with mineralocorticoid is a recognized cause of recurrent adrenal crises 3
• Inadequate mineralocorticoid replacement results in sodium wasting, volume depletion, and subsequent prerenal azotemia 3
• Postural hypotension specifically reflects insufficient mineralocorticoid therapy 3
• The combination of furosemide (which promotes sodium loss) with inadequate fludrocortisone creates a particularly high-risk situation for severe hyponatremia and adrenal crisis 3

Treatment Priorities

Treatment of suspected acute adrenal insufficiency should never be delayed by diagnostic procedures. 4 Immediate management includes:

• Hydrocortisone 100 mg IV bolus immediately upon clinical suspicion, as this dose saturates 11β-HSD type 2 to provide mineralocorticoid effect 1
• Aggressive fluid resuscitation with 0.9% isotonic saline at 1 liter over the first hour 1
• Draw blood for cortisol, ACTH, and electrolytes before treatment begins, but do not delay therapy waiting for results 1
• Fludrocortisone should be restarted when hydrocortisone dose falls below 50 mg/day during recovery, as lower doses no longer provide adequate mineralocorticoid effect 3, 1

The standard fludrocortisone replacement dose is 50-200 μg (0.05-0.2 mg) daily, usually taken as a single morning dose. 3, 6