The Role of Nuclear Medicine in the Clinical Management of Benign Thyroid Disorders, Part 2: Nodular Goiter, Hypothyroidism, and Subacute Thyroiditis

Part 2 of this series of Continuing Education articles on benign thyroid disorders deals with nodular goiter, hypothyroidism, and subacute thyroiditis. Togetherwith Part 1 (which dealtwith various forms of hyperthyroidism), this article is intended to provide relevant information for specialists in nuclear medicine dealing with the clinical management of patients with benign thyroid disorders, the primary audience for this series. Goiter, an enlargement of the thyroid gland, is a common endocrine abnormality. Constitutional factors, genetic abnormalities, or dietary and environmental factors may contribute to the development of nodulargoiter.Mostpatientswithnontoxicnodulargoiterareasymptomatic or have only mild mechanical symptoms (globus pharyngis).Workup of these patients includes measurement of thyroid-stimulating hormone, free triiodothyronine, free thyroxine, thyroid autoantibodies, ultrasoundimaging, thyroidscintigraphy,andfine-needleaspirationbiopsyof noduleswith certain ultrasoundandscintigraphic features.Treatment for multinodular goiter includes dietary iodine supplementation, surgery, radioiodine therapy (to decrease thyroid size), and minimally invasive ablation techniques. Hypothyroidism ranges from rare cases of myxedema to more common mild forms (subclinical hypothyroidism). Primary hypothyroidism often has an autoimmune etiology. Clinical presentations differ in neonates, children, adults, and elderly patients. Work-upincludes thyroid function tests andultrasoundimaging.Nuclear medicine is primarily used to locate ectopic thyroid tissue in congenital hypothyroidismor to detect defects in iodine organificationwith the perchlorate discharge test. Treatment consists of thyroid replacement therapy with L-thyroxine, adjusting the daily dose to the individual patient's metabolic and hormonal requirements. Subacute thyroiditis is a selflimited inflammatory disorder of the thyroid gland, often associated with painless or painful swelling of the gland and somatic signs or symptoms. Inflammationdisrupts thyroid follicles resulting in a rapid release of stored thyroxine and triiodothyronine causing an initial thyrotoxic phase, often followed by transient or permanent hypothyroidism.Although subacute thyroiditis is often related to a viral infection, no infective agent has been identified.Subacute thyroiditismay be caused by a viral infection in genetically predisposed individuals. Work-up includes lab tests, ultrasound imaging, and radionuclide imaging. Thyroid scintigraphy demonstrates different findings depending on the phase of the illness, ranging fromvery lowor absent tracer uptake in the thyroidglandin thehyperthyroidphase to a normalappearance in the late recoveryphase.Since subacute thyroiditis is self-limited, treatment is directed toward relief of pain. High-dose nonsteroidal antiinflammatory drugs are usually the first-line treatment. Ifseverepainpersists,acourseofcorticosteroidsmaybenecessary. Permanent hypothyroidism develops in up to 15% of patients with subacute thyroiditis, evenmore than 1 y after presentation.