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

Abstract

Goiter, an enlargement of the thyroid gland, is a common endocrine abnormality. Constitutional factors, genetic abnormalities, and/or dietary and environmental factors may contribute to the development of nodular goiter. Most patients with non-toxic nodular goiter are asymptomatic or have only mild mechanical symptoms (“globus pharyngis”). Work-up of these patients includes measurement of TSH, fT3, fT4, thyroid auto-antibodies, ultrasound imaging, thyroid scintigraphy, and fine-needle aspiration biopsy of nodules with certain ultrasound and scintigraphic features. Treatment for multinodular goiter includes dietary iodine supplementation, surgery, radioiodine therapy (to decrease thyroid size), and mini-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 the neonate, children, adults and elderly patients. Work-up includes thyroid function tests and ultrasound imaging. Nuclear medicine is primarily used to locate ectopic thyroid tissue in congenital hypothyroidism, or to detect defects in iodine organification with 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 self-limited inflammatory disorder of the thyroid gland, often associated with painless or painful swelling of the gland and somatic signs/symptoms. Inflammation disrupts thyroid follicles resulting in a rapid release of stored T4 and T3 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 thyroiditis may 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 from very low-to-absent tracer uptake in the thyroid gland in the hyperthyroid phase, to normal appearance in the late recovery phase. Since subacute thyroiditis is self-limited, treatment is directed toward relief of pain. High-dose nonsteroidal anti-inflammatory drugs are usually the first-line treatment. If severe pain persists, a course of corticosteroids may be necessary. Permanent hypothyroidism develops in up to 15% of patients with subacute thyroiditis, even more than 1 year following presentation.