Secondary hyperparathyroidism (2°HPT) is overactive parathyroid glands due to extra – parathyroid factors that stimulate otherwise normal parathyroid glands to be overactive. The two most common causes are kidney failure and vitamin D deficiency. 2°HPT is characterized by low normal or normal calcium levels and elevated PTH levels. Remember, 1°HPT is characterized by elevated calciumand elevated PTH levels.
With kidney failure a variety of changes occur in the body’s physiology that result in low calcium levels, low vitamin D activity and elevated phosphate levels. These alterations stimulate the parathyroid glands to release PTH. This chronic stimulation leads to enlargement of all the glands (hyperplasia). Usually, 2°HPT due to kidney failure is controlled with diet, medication and dialysis. Selected patient with symptoms of severe fatigue, bone pain, difficult to control hyperphosphatemia and PTH levels greater than 1000 are considered for surgery. This decision is made in consultation with the surgeon and nephrologist (kidney specialist).
Low vitamin D is another common cause of 2°HPT. A detailed discussion of vitamin D physiology is beyond our scope. Simply, vitamin D leads to increased calcium levels and a deficiency in vitamin D results in low calcium which then stimulates the parathyroid glands. Again, the calcium levels are in the low normal to normal range and the PTH levels are elevated. Treatment with vitamin D reverses these problems. Surgery does not play a role in treatment of this kind of 2°HPT.