Localization studies in patients with primary hyperparathyroidism

Primary hyperparathyroidism (HPT) is currently the most common cause of hypercalcaemia in ambulatory patients and is second only to cancer-related hypercalcaemia in hospitalized patients. Approximately 1 in every 1000 adults have HPT and the incidence is even higher in selected population groups such as elderly women in which 1 in 200 have been found to have this disease. The apparent increase in HPT is not due to an epidemic but rather to the ability to make the diagnosis, particularly in many asymptomatic patients. The widespread use of auto-analysers which included serum calcium levels, was the real factor that exposed the high incidence of this disease in the ambulatory patients. In current series, anywhere from 10 per cent to 50per cent of patients are considered to be ‘asymptomatic’. Nevertheless, there is a developing consensus that such patients should be operated upon unless there is a compelling medical contra-indication, because there is no way of predicting who will develop complications. Furthermore, there is increasing evidence that whereas parathyroidectomy prevents complications, it does not necessarily cure them once they are established. There has been considerable debate about the utilization of localization studies, once the diagnosis is firmly established by biochemical testing, in patients who have not been previously explored. This has intensified with the development of noninvasive studies such as ultrasonography, technetium-thallium scintigraphy , CT and MRI scanning. It is argued that the demonstration of a suspected enlarged parathyroid by these techniques confirms the diagnosis and reassures the patient, referring physician, and surgeon that the diseased gland(s) will be found and appropriately treated. A few experienced surgeons also believe that a unilateral cervical exploration is appropriate when a single enlarged gland is found at operation in addition to an ipsilateral normal gland. Although this opinion does not represent the majority view, it is an argument used in justification for pre-operative localization in patients about to undergo their first operation. It is true that the sensitivity of localization studies has improved and they are of great value when positive in planning reoperative parathyroid explorations in which anatomical changes from a previous exploration markedly increase the difficulty and the potential morbidity’-3. Nevertheless, localization techniques can be misleading and none alone, or in combination, compares favourably with results obtained by an experienced parathyroid surgeon carrying out a primary exploration. At best, localization procedures will demonstrate or localize the diseased gland in approximately 80percent of cases. Their reliability is far less in patients with hyperplasia or multiple gland disease and in those with adenomas smaller than 1 cm in diameter. They are particularly likely to give false negative findings in patients who have asymptomatic or uncomplicated disease or in patients with kidney stones whose calcium levels may be barely above the upper range of normal. False positive studies can also mislead or misdirect the inexperienced surgeon: as an example, thallium scans may be positive in patients with a variety of thyroid lesions including medullary carcinoma and some differentiated carcinomas as well as microfollicular adenoma. The routine use of these studies in primary cases merits critical appraisal. High-resolution ultrasonography has been found to have good specificity (95 per cent) and a sensitivity of approximately 75-80 per cent for adenomas larger than 1 cm. It is non-invasive, readily available and free of radiation. Its limitations are related to the location of adenomas; those in the retrotracheal and retro-oesophageal areas as well as in the mediastinum are usually not detected. Thyroid abnormalities, particularly multinodular goitres, decrease the sensitivity and specificity of the test. The specificity when positive approaches 95 per cent. Ultrasonography is best in demonstrating adenomas in juxtaposition to the lower pole of the thyroid gland. However, these are the easiest for the surgeon to detect at operation. Thallium-technetium scintigraphy has a sensitivity of approximately 75 per cent and specificity of 90 per cent in primary cases. Again, thyroid abnormalities decrease the sensitivity and specificity and posteriorly located glands can be missed, regardless