Primary hyperparathyroidism vs Malignancy hypercalcemia
How to tell Primary hyperparathyroidism and Malignancy hypercalcemia apart when a board question makes them look alike.
High PTH means parathyroid source; low PTH means look for malignancy or another non-PTH cause.
Side by side
Hypercalcemia with inappropriately high PTH, kidney stones, bone pain, or psychiatric/GI symptoms.
Hypercalcemia with suppressed PTH, weight loss, cancer history, PTHrP, or lytic bone lesions.
Autonomous parathyroid hormone secretion raises calcium.
Tumor factors or bone destruction raise calcium independent of parathyroid hormone.
High calcium plus high PTH supports primary hyperparathyroidism.
High calcium plus low PTH supports malignancy hypercalcemia.
The trap
Symptoms of hypercalcemia (stones, bones, abdominal moans, psychiatric overtones, polyuria, constipation) are identical in both. The deciding test is PTH measured at the same time as calcium. High or inappropriately normal PTH for an elevated calcium equals primary hyperparathyroidism (usually a solitary parathyroid adenoma, often discovered incidentally, more common in older women, often asymptomatic). Suppressed (low) PTH with high calcium equals malignancy hypercalcemia. If PTH is suppressed, check PTHrP (humoral hypercalcemia of malignancy from squamous cell lung cancer, breast cancer, renal cell carcinoma), 1,25-vitamin D (granulomatous diseases and lymphomas), and bone scan or CT for lytic metastatic disease.
Watch it explained
The repair move
For any hypercalcemia, measure PTH at the same time as calcium and walk the algorithm: (1) high or inappropriately normal PTH with high calcium equals primary hyperparathyroidism (work up for adenoma vs MEN1 / MEN2A); (2) suppressed PTH with high calcium triggers a non-PTH workup: PTHrP for humoral hypercalcemia of malignancy, 1,25-vitamin D for lymphoma and granulomatous disease, bone scan for lytic metastatic disease, 24-hour urine calcium (familial hypocalciuric hypercalcemia gives low urine calcium with mildly elevated PTH); (3) treat hypercalcemic crisis (calcium above 14 mg/dL) with aggressive IV normal saline at 200 to 300 mL/hr, calcitonin for rapid effect over 24 to 48 hours, and IV bisphosphonate (zoledronic acid) for sustained reduction.
Try a free question
CoreA patient has recurrent kidney stones, bone pain, high calcium, low phosphate, and inappropriately elevated PTH. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Primary hyperparathyroidism. High calcium with high PTH points to primary hyperparathyroidism.
Why the other choices are tempting
- B. Malignancy hypercalcemia suppresses endogenous PTH.
- C. Vitamin D intoxication raises calcium with suppressed PTH.
- D. Sarcoidosis can raise vitamin D activation and suppress PTH.
- E. Milk-alkali syndrome causes hypercalcemia with alkalosis and suppressed PTH.
Flashcards
Tap a card to flip it.
What is the first lab branch in hypercalcemia?
PTH decides whether the calcium problem is parathyroid-driven or coming from a non-PTH source.
How does PTH raise serum calcium?
It increases bone resorption, renal calcium reabsorption, phosphate wasting, and 1-alpha hydroxylase activity that raises active vitamin D.
Quick answers
What is the fastest way to tell Primary hyperparathyroidism from Malignancy hypercalcemia?
High PTH means parathyroid source; low PTH means look for malignancy or another non-PTH cause.
What is the key clue for Primary hyperparathyroidism?
Hypercalcemia with inappropriately high PTH, kidney stones, bone pain, or psychiatric/GI symptoms.
What is the key clue for Malignancy hypercalcemia?
Hypercalcemia with suppressed PTH, weight loss, cancer history, PTHrP, or lytic bone lesions.
What is the common trap with Primary hyperparathyroidism vs Malignancy hypercalcemia?
Symptoms of hypercalcemia (stones, bones, abdominal moans, psychiatric overtones, polyuria, constipation) are identical in both. The deciding test is PTH measured at the same time as calcium. High or inappropriately normal PTH for an elevated calcium equals primary hyperparathyroidism (usually a solitary parathyroid adenoma, often discovered incidentally, more common in older women, often asymptomatic). Suppressed (low) PTH with high calcium equals malignancy hypercalcemia. If PTH is suppressed, check PTHrP (humoral hypercalcemia of malignancy from squamous cell lung cancer, breast cancer, renal cell carcinoma), 1,25-vitamin D (granulomatous diseases and lymphomas), and bone scan or CT for lytic metastatic disease.