[Clinical nuclear medicine in thyroid diseases]

Area of Science:

• Endocrinology
• Nuclear Medicine
• Immunology

Background:

• Thyroid disease diagnosis relies on various isotopic tests.
• In vitro tests measure serum hormone levels (T4, T3, TSH) and antibodies.
• In vivo tests like scintigraphy provide functional thyroid information.

Purpose of the Study:

• To review current in vitro and in vivo isotopic diagnostic methods for thyroid diseases.
• To highlight advancements in radioassays for thyroid antibodies and hormone measurements.
• To discuss the utility of thyroid scintigraphy in differential diagnosis.

Main Methods:

• In vitro: Radioimmunoassay (RIA), Immunoradiometric Assay (IRMA), Radio-receptor Assay (RRA) for hormones and antibodies (TSH receptor, anti-Tg, anti-TPO).
• In vivo: Thyroid scintigraphy using Iodine-123 (123I) or Technetium-99m (99mTc), assessing uptake rates and tumor imaging.
• Specific assays mentioned include TSAb for antibody activity, RIA/IRMA for thyroglobulin (Tg), and RIA for free T4 (FT4).

Main Results:

• New radioassays offer improved sensitivity for early diagnosis of Hashimoto's thyroiditis and detection of anti-Tg antibodies.
• IRMA allows accurate Tg measurement even with interfering anti-Tg antibodies.
• Advanced FT4 assays overcome limitations related to albumin and anti-T4 antibodies.
• Thyroid scintigraphy aids in differentiating Graves' hyperthyroidism from destructive thyrotoxicosis.
• Increased radioisotope uptake in hypothyroid patients suggests dyshormonogenesis or iodine-induced hypothyroidism.

Conclusions:

• Isotopic tests are crucial for comprehensive thyroid disease diagnosis.
• Recent advancements in radioassay technology enhance diagnostic accuracy and sensitivity.
• In vivo and in vitro isotopic methods provide complementary information for effective patient management.