Sestamibi Scans: what is it and when is it needed?

Typically, the diagnosis of hyperparathyroidism is an incidental finding. As part of a thorough assessment, blood work is often done and the serum calcium value (also called blood calcium level) is found to be high. Whenever the serum calcium value is found to be elevated, assessment and determination of the source is indicated.

The initial tests to confirm parathyroid disease are often done at a parathyroid treatment center, which could be the office of an endocrinologist or otolaryngologist. These include a parathyroid hormone blood test and a calcium level blood test. If these levels indicate hyperparathyroidism, additional testing will be needed prior to treatment for parathyroid disease.

The testing will often include a nuclear medicine scan in addition to assessment of serum calcium value. The purpose of a nuclear scan is to identify which of the four parathyroid glands is involved. There are four parathyroid glands located right behind the thyroid gland and in most cases only one of the four glands is abnormal. In over 90% of the patients, three of their four glands will be normal but one will be enlarged and present. A negative scan means that the abnormal gland or abnormal glands did not take up the sestamibi. The nuclear medicine scan called the sestamibi scan is used to identify which of the glands is abnormal. A positive scan shows that the gland is overactive. The scan may be positive for one out of four or may be positive for all four glands. When all four glands are considered positive, the implication is that all four glands are abnormally enlarged. This condition is called parathyroid hyperplasia. In this situation, the disease involves all four parathyroid glands and removal of parts of all of these glands would be essential for complete cure. Treatment of hyperplasia is far more complicated than treatment of a parathyroid adenoma and only parathyroid surgical specialists should deal with treatment of parathyroid hyperplasia.

A negative scan is also a relatively common finding. It does not mean that the patient does not have hyperparathyroidism. Approximately 15% of patient with primary hyperparathyroidism have negative scans. In cases of a negative scan, the surgeon explores all the four parathyroid glands and identifies the abnormal gland with direct visualization.