Electrolytes

Question 1

In asymptomatic patient with hyponatremia 2/2 SIADH what is the best management? Why? What would giving NS do? What is the most helpful test to assess the status of ADH on the kidney?

Answer 1

In asymptomatic patients with hyponatremia secondary to the syndrome of inappropriate antidiuretic hormone (SIADH), the most appropriate first step in management is to fluid restrict.

In SIADH fluid restriction will result in loss of free water through respiration and sweating, and eventual concentration of the patient’s serum. If this is unsuccessful, then other interventions include salt tablets and medication management. These will generally be performed under the supervision of a nephrologist depending on the severity. Contrary to what some may think, giving normal saline, though having a higher concentration of sodium than the serum, will not help a patient with SIADH and actually will make things worse as the kidney will excrete concentrated urine and retain the free water with a net loss of sodium. Only very concentrated sodium solutions, such as 3%, will effectively raise the serum sodium.

When assessing hyponatremia, the history and examination are important. The urine osmolality is most helpful for determining if ADH is elevated.

Question 2

What is the most common cause of Hypercalcemia in an otherwise healthy patient?

Answer 2

The most common cause of hypercalcemia in an otherwise healthy, ambulatory patient is hyperparathyroidism. The most common clinical presentation of primary hyperparathyroidism (PHPT) is asymptomatic hypercalcemia. The diagnosis is usually first suspected because of the incidental finding of elevated serum calcium on biochemical screening tests.

In addition, PHPT may be suspected in a patient with recurrent nephrolithiasis. The initial diagnostic workup generally includes repeating the serum calcium with albumin correction or obtaining an ionized calcium test to confirm that hypercalcemia is actually present. Recall that calcium is bound to albumin, and the level of serum albumin can affect the laboratory interpretation of serum calcium. The lower the albumin, the lower the normal serum calcium. This correction can be avoided with a direct ionized calcium measurement.

If hypercalcemia is confirmed, then serum calcium should be redrawn with an intact parathyroid hormone (PTH) to evaluate the parathyroid response. If the calcium and PTH are both elevated, then hyperparathyroidism is confirmed. If the PTH is normal or only minimally elevated, then vitamin D should be measured, and urinary calcium excretion can be evaluated. If the PTH is normal or low, then this is concerning for non-PTH mediated hypercalcemia, and vitamin D, as well as PTH-related peptide, should be measured

Question 3

What are some causes of hyperparathyroidism

Answer 3

Potential Causes of Hyperparathyroidism

Parathyroid mediated
Primary hyperparathyroidism
Inherited variants (like multiple endocrine neoplasia syndrome)
Familial hypocalciuric hypercalcemia
Tertiary hyperparathyroidism (renal failure)

Non-parathyroid mediated
Hypercalcemia of malignancy
Osteolytic bone metastases
Vitamin D intoxication

Medications
Thiazide diuretics
Lithium
Excessive vitamin A

Miscellaneous
Hyperthyroidism
Acromegaly
Pheochromocytoma
Adrenal insufficiency
Immobilization
Parenteral nutrition

Question 4

In patient with Nephrogenic DI what diuretic can be used?

Answer 4

Thiazide diuretics in combination with a low-solute diet can diminish the degree of polyuria in patients with nephrogenic DI. The potassium-sparing diuretic amiloride may be helpful, both because of its additive effect with the thiazide diuretic and in this case of a reversible lithium-induced disease, by possibly allowing lithium to be continued.