Can hyperparathyroidism and adrenal cortical insufficiency cause hyponatremia?

Can Hyperparathyroidism and Adrenocortical Insufficiency Cause Hyponatremia?

Yes, adrenocortical insufficiency is a well-established cause of hyponatremia, while hyperparathyroidism does not directly cause hyponatremia but rather causes hypercalcemia.

Adrenocortical Insufficiency and Hyponatremia

Primary Adrenal Insufficiency (Addison's Disease)

Hyponatremia is present in 90% of newly presenting cases of primary adrenal insufficiency (PAI). 1 This makes it one of the most consistent laboratory findings in this condition.

Mechanism of hyponatremia in adrenal insufficiency: 1

• Loss of sodium in urine due to aldosterone deficiency
• Increased plasma vasopressin levels despite hypo-osmolality
• Increased angiotensin II, which impairs free water clearance
• The combination creates a euvolemic hyponatremia picture

Key diagnostic features: 1

• Hyponatremia is often only marginally reduced at presentation
• The classic combination of hyponatremia AND hyperkalemia occurs in only approximately 50% of patients at diagnosis
• Serum cortisol is usually below normal range with clearly increased plasma ACTH
• Between 10-20% of patients have mild to moderate hypercalcemia (not hyponatremia) at presentation 1

Secondary Adrenal Insufficiency (Hypopituitarism)

Secondary adrenal insufficiency from hypopituitarism is a frequently overlooked cause of severe hyponatremia that requires high clinical suspicion. 2, 3

In a retrospective study of 185 patients with severe hyponatremia (<130 mmol/l), 28 patients had hypopituitarism with secondary adrenal insufficiency, and in 25 of these cases the diagnosis had not been previously recognized. 3 Twelve patients had recurrent hyponatremia during previous hospital admissions (up to four times) before the correct diagnosis was made. 3

Clinical presentation is often subtle: 3

• Mean age 68 years (21 women, 7 men)
• Missing or scanty pubic and axillary hair
• Pale and doughy skin
• Small testicles in men
• Symptoms overlap with SIADH: nausea, vomiting, confusion, disorientation, somnolence or coma

Critical diagnostic distinction: 4, 5

• Glucocorticoid deficiency presents with euvolemic hyponatremia and inappropriate urinary concentration—identical to SIADH
• The original diagnostic criteria for SIADH emphasized that normal adrenal reserve is essential for its diagnosis
• Despite this, clinicians frequently ignore plasma cortisol measurement in both clinical practice and research protocols 4

Basal serum cortisol levels in acutely ill hyponatremic patients with hypopituitarism ranged from 20-439 nmol/l (mean 157±123), while in other severely hyponatremic patients without adrenal insufficiency it ranged from 274-1732 nmol/l (732±351 nmol/l). 3

Hyperparathyroidism and Electrolyte Abnormalities

Hyperparathyroidism causes hypercalcemia, NOT hyponatremia. 6, 7

The relationship between hyperparathyroidism and hyponatremia is indirect: 8

• A case report described transient hyponatremia as the first symptom of MEN-1 syndrome, but the hyponatremia was due to secondary adrenal insufficiency from a pituitary tumor, not from the hyperparathyroidism itself 8
• The hyperparathyroidism in that case was asymptomatic and manifested as hypercalcemia 8

Conversely, adrenal insufficiency can cause hypercalcemia: 1, 9

• Between 10-20% of patients with primary adrenal insufficiency have mild to moderate hypercalcemia at presentation 1
• Hypercalcemia secondary to adrenal insufficiency is rare but well-documented and often remains underdiagnosed 9

Clinical Pitfalls and Recommendations

Common diagnostic errors to avoid:

1. Assuming SIADH without checking cortisol: 4, 5

   • Thyroid function was tested in only 69% and adrenal function in only 29% of euvolemic hyponatremia cases in one real-world study 5
   • Both hypoadrenalism and hypothyroidism are easily treatable, potentially life-threatening conditions 5

2. Dismissing transient or mild hyponatremia: 8

   • Spontaneous improvement of laboratory abnormalities should not be assumed to be false or unimportant
   • Transient hyponatremia may be the first clue to serious endocrine disease

3. Missing recurrent presentations: 3

   • Patients with undiagnosed hypopituitarism may present with recurrent hyponatremia multiple times before diagnosis

Mandatory workup for euvolemic hyponatremia: 1, 2, 4

• Paired measurement of serum cortisol and plasma ACTH
• Thyroid function tests (TSH, FT4)
• In equivocal cases, synacthen stimulation test (0.25 mg IM or IV) with peak serum cortisol <500 nmol/L diagnostic of PAI 1

Treatment response confirms diagnosis: 3

• All patients with hyponatremia due to hypopituitarism recovered after low-dose hydrocortisone substitution
• Hyponatremia typically resolves within 1-3 days after hormone replacement therapy 5