Benign thyroid disease: what is the role of nuclear medicine?

Nuclear medicine is directly involved in both the diagnosis and treatment of benign thyroid disease, which requires an understanding of the pathophysiology and management of thyroid disorders in addition to expertise in nuclear methodology. Thyroid uptake and imaging, the principal nuclear tests in thyroid disease, may be used as follows: (1) Differential diagnosis of hyperthyroidism: A very low thyroid uptake suggests destructive ("subacute") thyroiditis, a self-limited disorder, whereas a normal or elevated uptake is consistent with toxic nodular goiter and Graves' disease. Scintigraphic characteristics also help differentiate between nodular and Graves' disease. (2) Function of thyroid nodules: Fine-needle aspiration biopsy with cytological examination (FNAB) is used routinely to assess for malignancy in thyroid nodules. Scintigraphy may be of assistance before FNAB. "Hot" nodules are generally benign and do not require FNAB, while "cold" nodules may be malignant. (3) Differential diagnosis of congenital hypothyroidism: Scintigraphy combined with ultrasound examination may be used to identify such conditions as thyroid agenesis, dyshormonogenesis, and incomplete thyroid descent. Treatment of Graves' disease and toxic nodular disease with (131)I may require greater clinical involvement and decision analysis compared with thyroid uptake and imaging. The following aspects of treatment are particularly important: (1) Risk: Radioiodine treatment may occasionally aggravate hyperthyroidism, Graves' ophthalmopathy, and airway obstruction caused by large, nodular goiters. Alternative treatments, including the temporary use of antithyroid drugs, and surgery for nodular goiters, may be considered. (2) Radioiodine dose: Cure of hyperthyroidism with a single (131)I treatment is desirable, though not always possible. Such factors as a large goiter, severe hyperthyroidism, and prior propylthiouracil therapy, may contribute to treatment failure. (3) Informed consent: A detailed discussion with the patient regarding the clinical risks, outcomes, and side effects of (131)I is a critical component of successful management.

Comparison of (123)I and (131)I for whole-body imaging in thyroid cancer.

UNLABELLED: We compared the diagnostic sensitivities of (123)I and (131)I whole-body imaging in differentiated thyroid cancer. METHODS: Twelve thyroidectomized patients (3 previously treated with (131)I) were studied. After a period of thyroid hormone withdrawal, whole-body imaging was performed approximately 24 and 72-96 h after administration of 74-185 MBq (2-5 mCi) (123)I and 111-185 MBq (3-5 mCi) (131)I, respectively. RESULTS: Both (123)I and (131)I revealed residual thyroid tissue, present in 9 patients. (131)I detected metastases in 5 studies of 4 patients. In 4 of 5 studies, (123)I missed metastases shown by (131)I in 8 body regions including the neck, mediastinum, lungs, and bone and detected 3 other sites of metastasis only in retrospect. No lesion was better seen with (123)I than with (131)I. CONCLUSION: Although (123)I is adequate for imaging residual thyroid tissue, it appears to be less sensitive than (131)I for imaging thyroid cancer metastases.