From the Guidelines
The correct answer is C. Hypercalcemia, as it is the most common electrolyte abnormality associated with malignancy, particularly in lung cancer, occurring in approximately 10-25% of patients with lung cancer 1.
Key Points
- Hypercalcemia of malignancy is characterized by a suppressed intact parathyroid hormone (iPTH) level and a low or normal calcitriol level 1.
- The symptoms described in the case, such as confusion and constipation, are classic manifestations of hypercalcemia, which can also include nausea, vomiting, polyuria, polydipsia, and in severe cases, cardiac arrhythmias and coma.
- In lung cancer specifically, the most common mechanism of hypercalcemia is parathyroid hormone-related protein (PTHrP) secretion, which increases bone resorption and renal calcium reabsorption, leading to elevated serum calcium levels 1.
Management
- Treatment typically involves aggressive hydration, bisphosphonates, calcitonin, and addressing the underlying malignancy 1.
- Oral hydration may be effective in mild hypercalcemia, while moderate to severe hypercalcemia requires rehydrating with IV crystalloid fluids not containing calcium and giving loop diuretics (eg, furosemide) as needed after correction of intravascular volume 1.
- Bisphosphonates (clodronate, pamidronate, and zoledronic acid) are usually effective, and additional therapeutic options such as glucocorticoids, gallium nitrate, and salmon calcitonin may be considered 1.
From the Research
Electrolyte Abnormalities in Malignancy
The patient's symptoms of confusion and constipation, along with laboratory results confirming an electrolyte imbalance, suggest a possible connection to the underlying malignancy.
- The most common electrolyte abnormalities associated with malignancy include:
- Hyponatremia
- Hypoglycemia
- Hypercalcemia 2
- Hypercalcemia is a notable electrolyte abnormality that can occur in patients with malignancy, particularly in those with lung cancer 3, 4, 5
- Tumor-induced hypercalcemia (TIH) is often associated with parathyroid hormone-related protein (PTHrP) 3, 4, 5
- The presence of hypercalcemia in lung cancer patients can be an ominous prognostic sign 3
Specific Electrolyte Abnormalities
Considering the options provided:
- Hypercalcemia (C) is the most commonly associated electrolyte abnormality with malignancy, particularly in lung cancer patients 3, 4, 5
- Hyponatremia (A) is also a common electrolyte abnormality in cancer patients, but it is not as specifically associated with lung cancer as hypercalcemia 2, 6
- Hypokalemia (B) and hypomagnesemia (D) are not as frequently associated with malignancy as hypercalcemia 2, 6