A biopsy of the parathyroid gland may show a tumor or hyperplasia. In primary hyperparathyroidism an increased secretion of parathyroid hormone occurs because of enlargement of one or more of the glands secondary to the presence of a tumor, a parathyroid adenoma, resulting in high plasma calcium levels. In secondary hyperparathyroidism there is an increased activity of the parathyroid gland with excessive production of parathyroid hormone in response to an abnormality outside the parathyroid gland producing low plasma calcium levels. An increase in the cells of the parathyroid glands, called hyperplasia, occurs which is responsible for the elevation of parathyroid hormone levels. The causes of this disorder include rickets , vitamin D deficiency , or chronic renal failure .
Secondary hyperparathyroidism is the most common cause of hyperparathyroidism in children.
The incidence of mild secondary hyperparathyroidism is 1 out of 1000 people. The incidence of severe hyperparathyroidism is 1 out of 10,000 people. Early detection of rickets or vitamin D deficiency may prevent secondary hyperparathyroidism.