Diagnosis of occult familial medullary carcinoma of the thyroid using pentagastrin.

Medullary carcinoma of the thyroid is unique in that it can often be diagnosed solely on the basis of abnormally high basal serum thyrocalcitonin levels. Two brothers described in this report were found to have normal basal serum thyrocalcitonin levels when examined after another family member died from metastatic medullary carcinoma of the thyroid. Pentagastrin, a synthetic analog of gastrin, was subsequently administered to these two high-risk relatives and found to stimulate the release of thyrocalcitonin to abnormally high levels. They were found to have occult medullary carcinoma of the thyroid. Eight other first-degree relatives of the deceased patient with normal basal serum thyrocalcitonin levels were screened with pentagastrin and found to have normal stimulated levels of thyrocalcitonin. This report reinforces the need to recognize that medullary carcinoma of the thyroid can be familial and that physicians are obligated to screen asymptomatic kin who are at high risk. We recommend that all susceptible relatives, even if they have normal basal serum thyrocalcitonin levels, undergo the provocative pentagastrin test with repeat annual testing if necessary. In addition, the provocative pentagastrin test can be used to follow up patients who have undergone thyroidectomy.