All are TRUE about hyperparathyroidism, except –
**Core Concept**
Hyperparathyroidism is a disorder of calcium and phosphate metabolism caused by an overproduction of parathyroid hormone (PTH) by one or more of the parathyroid glands. This excess PTH leads to increased calcium levels in the blood, which can cause a variety of symptoms and complications.
**Why the Correct Answer is Right**
Option C: Hyperparathyroidism is indeed characterized by an increased level of PTH, which in turn causes hypercalcemia (elevated calcium levels in the blood). The increased PTH levels stimulate the release of calcium from bones, increase calcium absorption from the gut, and decrease calcium excretion by the kidneys.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because primary hyperparathyroidism is typically caused by a single parathyroid gland becoming overactive, not all four glands. While it's possible for all four glands to be affected in some cases, this is less common.
**Option B:** This option is incorrect because while hyperparathyroidism can cause an increase in calcium levels, it does not typically cause hyperphosphatemia (elevated phosphate levels). In fact, the increased PTH levels in hyperparathyroidism usually lead to decreased phosphate levels in the blood.
**Option D:** This option is incorrect because while hyperparathyroidism can cause bone resorption and osteoporosis, it is not a direct cause of renal failure. However, chronic hypercalcemia can cause kidney stones and damage the kidneys over time.
**Clinical Pearl / High-Yield Fact**
A key clinical feature of primary hyperparathyroidism is the presence of a "classic" hypercalcemic syndrome, which includes hypercalcemia, hypophosphatemia, and an increased alkaline phosphatase level. This syndrome is often seen in patients with a history of kidney stones.
**Correct Answer: A. Primary hyperparathyroidism is typically caused by a single parathyroid gland becoming overactive.**