Surgical biopsy result: blood, few cells, no sign of lymphoma or other recognizable tumor.
Routine labs reveal elevated serum Ca: Total 11.9 (Normal: 8.8 - 10.5); Ionic 1.56 (Normal: 1.13 - 1.32)
Parathyroid adenoma is a benign neoplasm of the parathyroid which usually comes to clinical attention because of overproduction of parathyroid hormone.
Parathyroid adenomas are thought to be the result of a somatic mutation in a parathyroid cell which results in a clonal expansion of mutant cells. A variety of different chromosomal deletions have been demonstrated in different adenomas, with probable deletion of tumor suppressor genes. The incidence increases in those exposed to neck irradiation, with a lag time of decades, but in most cases, no history of mutagen exposure is elicited.
The disease occurs in all age groups but has its peak incidence between the 3rd and 5th decades, with an estimated annual incidence of 2 per 1000 population. However, the clinical course is variable, with some cases remaining essentially asymptomatic, and others presenting acutely with severe dehydration and even coma, the hypercalcemic parathyroid crisis. Excessive levels of parathyroid hormone lead to presenting features such as nephrolithiasis and impaired renal function, peptic ulcers, mental status changes, and bone resorption, leading to osteitis fibrosa cystica and, in some patients, osteopenia. Bone involvement tends to affect cortical bone more than trabecular bone. Other manifestations include proximal muscle weakness and atrophy, chondrocalcinosis, and pseudogout.
The diagnosis of primary hyperparathyroidism is typically confirmed by direct measurement of circulating PTH levels by immunoassay. The first line therapy for symptomatic patients is surgical excision. The surgery is low-risk, curative, and has a success rate of over 90% in experienced hands. Asymptomatic patients, particularly older patients who wish to avoid surgery may be followed.
In many practices, resectional surgery is undertaken without the use of prior imaging. Since about 80% of cases are due to a solitary adenoma, when such a tumor is found by exploration and removed, and if normal parathyroid tissue can be demonstrated in at least one other gland (to exclude cases of chief cell parathyroid hyperplasia), chances of success are good. However, this approach will fail in the case of multiple adenomas. At the other extreme, even when all four glands are identified at surgery, there are documented cases of presence of 5 or 6 glands, and ectopically located glands (e.g: mediastinal) are not rare. To avoid failures in such cases, or to rectify them at re-operation, imaging can be helpful.
Imaging techniques include ultrasound, CT, angiography, and of course, scintigraphy. Ultrasound and CT can identify nodular structures, and differentiate solid tissue from cysts, but cannot distinguish between a thyroid nodule, a lymph node, and a parathyroid adenoma.
Scintigraphy can be used to distinguish between thyroid and parathyroid tissue, and identify larger than normal foci of parathyroid tissue. Two methods are in use. The method used in the case presented uses sestamibi, which is taken up by both thyroid and parathyroid tissue, but washes out of the thyroid relatively rapidly, leaving predominantly parathyroid activity on delayed images. An older method uses a combination of images obtained with two tracers; a pertechnetate image, depicting only thyroid uptake, is subtracted from a thallium image, which depicts the combination of thyroid and parathyroid uptake. The difference image represents foci of parathyroid tissue.
Isselbacher, K. et. al, Harrison’s Principles of Internal Medicine, 13th Ed., McGraw-Hill, 1994.
Murray, I.P.C, Ell, P.J. Nuclear Medicine in Clinical Diagnosis and Treatment, 2nd Ed. Churchill-Livingstone, 1999.
Wilson, J.D. et al, Williams Textbootk of Endocrinology, 9th Ed., W.B. Saunders, Philadelphia 1998.
Click here to go to Joint Program in Nuclear Medicine home page and Copyright notice.