Secondary hyperparathyroidism

Secondary hyperparathyroidism refers to the excessive secretion of parathyroid hormone (PTH) by the parathyroid glands in response to hypocalcemia (low blood calcium levels) and associated hypertrophy of the glands. This disorder is especially seen in patients with chronic renal failure. It is often--although not consistently--abbreviated as SHPT in medical literature.

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Signs and Symptoms

Bone and joint pain are common, as are limb deformities. The elevated PTH has also pleiotropic effects on blood, immune system and neurological system.

Diagnosis

The PTH is elevated due decreased levels of calcium or 1,25-dihydroxy-vitamin D3. It is usually seen in cases of chronic renal disease or defective calcium receptors on the surface of parathyroid glands.

Causes

Chronic renal failure is the most common causes of secondary hyperparathyroidism. Failing kidneys do not convert enough vitamin D to its active form, and they do not adequately excrete phosphorus. When this happens, insoluble calcium phosphate forms in the body and removes calcium from the circulation. Both processes leads to hypocalcemia and hence secondary hyperparathyroidism.

Treatment

If the underlying cause of the hypocalcemia can be addressed, the hyperparathyroidism will resolve. In patients with chronic renal failure, older treatments consists of dietary restriction of phosphorus, supplements with the active form of vitamin D, and phosphate binders. In recent years, a newer class of medications, calcimimetics cinacalcet, have achieved amazing response rates and has reduced the number of patients who eventually require surgery. Some of these patients may also see resolution of their sHPT following kidney transplantation.

Prognosis

If left untreated, the disease will progress to tertiary hyperparathyroidism, where correction of the underlying cause will not stop excess PTH secretion, i.e. parathyroid gland hypertrophy becomes irreversible.

See also

• Primary hyperparathyroidism
• Tertiary hyperparathyroidism