PA 2-Thyroid and parathyroid function assessment laboratory tests, external radionuclide scan, ultrasonography(1)
Page 1: Title and Overview
Title: Thyroid and Parathyroid Function Assessment
Faculty: Faculty of Medicine in English
Assessment methods: Laboratory tests, external radionuclide scan, ultrasonography
Discipline: Physiology
Year of study: 3
Page 2: Anatomy of the Thyroid Gland
Location: Anterior neck, across the front of the trachea
Weight: Approximately 20g in adults
Structure: Composed of left and right lobes, and a connecting isthmus
Hormone production:
Thyroid Hormones: T4 (Thyroxine), T3 (Triiodothyronine)
Calcitonin
Page 3: Anatomy Illustration
Anatomical Structures:
Veins: Internal jugular vein
Trachea and associated muscles: Thyrohyoid muscle, Thyroid cartilage, Cricoid cartilage
Nerves: Vagus nerve, Right recurrent laryngeal nerve
Other Structures: Esophagus, Common carotid artery, Vertebral body
Lobes of the Thyroid: Right lobe, Left lobe, Isthmus
Page 4: Hormone Physiology
Essential Trace Element: Iodine needed for T4 and T3 production
Storage: Hormones stored in thyroid colloid, mainly in the form of thyroglobulin
Hormones:
Tetraiodothyronine (T4 or Thyroxine)
Triiodothyronine (T3)
Page 5: Thyroid Cell Structures
Thyroglobulin: Surrounds thyroid follicular cells, synthesized therein
C Cells (Parafollicular Cells): Produce calcitonin, role in calcium and phosphate homeostasis
Page 6: Reference Note
Author and Source: George Emil Palade, University of Medicine, Pharmacy, Science and Technology of Târgu Mureș
Page 7: Hormone Production Mechanism
Process Overview:
TSH binds to receptors on follicular cells
Endocytosis of colloid droplets occurs
Lysosomal digestion of droplets forms T4 and T3
Secretion into circulation
Conversion: T4 (80%) converted to T3 (35%) in target cells by 5′-deiodinase
Page 8: Synthesis Steps of Thyroid Hormones
Iodide trapping from blood
Oxidation of iodide to iodine
Organification: Iodine added to tyrosine
Coupling: Formation of T3 and T4 from iodotyrosines
Page 9: Hormone Binding and Activity
Circulation: T4 and T3 primarily bound to proteins
Biologically Active Form: Free T3 mediates effects on target tissues, regulates feedback on pituitary and hypothalamus
Major Binding Protein: Thyroxine-binding globulin (TBG) produced in the liver
Page 10: Regulation of T3 and T4
TRH is released by the brain
Stimulates TSH from pituitary gland
TSH prompts iodine uptake and T3, T4 release
Feedback mechanism: High free T3 and T4 suppress TSH release
Page 11: Recommendations for Screening
High-Risk Groups: Neonates, pregnant/postpartum females, elderly, family history of thyroid disease
Diagnostic Measure: TSH and free thyroxine (fT4) levels are essential for diagnosis of hyperthyroidism and hypothyroidism
Key Indicator: FT4 as a reliable indicator
Page 12: Characterizing Disorders
Types of Disorders:
Primary: Originates in the thyroid
Secondary: Originates in the pituitary
Tertiary: Originates in the hypothalamus
Page 13: Sample Collection for Thyroid Function Tests
Sample Type: Serum or plasma, preferably free from hemolysis and lipemia
Newborn Screening: Whole blood collected by heel puncture
Storage: Sample kept at 2 to 8°C if not analyzed within 24 hours
Page 14: Battery of Tests for Thyroid Function
Tests Include:
TSH
Free thyroxine (fT4)
Total thyroxine (TT4)
Free triiodothyronine (fT3)
Total triiodothyronine (TT3)
Thyroglobulin
Thyroid antibodies
Thyroxine-binding globulin (TBG)
Page 15: Hormone Level Measurement Methods
Immunoassays: High sensitivity for low hormone levels
Importance of specificity in clinical settings, ensuring accurate measurement of thyroid hormones
Page 16: Radioimmunoassay (RIA) Process
Description of the steps in the RIA process for measuring hormone levels in serum
Antibody binding and separation from unbound hormone
High specific radioactivity indicates higher levels of hormones in patient serum
Page 17: TSH Screening and Interpretation
TSH Levels: Interpretation:
Increased TSH + increased fT4: secondary causes of thyrotoxicosis
Increased TSH + low fT4: primary hypothyroidism
Low TSH + low fT4: secondary hypothyroidism
Low TSH + high fT4: primary hyperthyroidism
Page 18: Measurement Techniques for Total T4 and T3
Techniques: RIA, chemiluminometric assay
Importance of Measuring Free Hormones: Alteration in protein binding can skew total hormone levels
Page 19: Analysis of Free Hormone Levels
Free Hormone Levels (fT4, fT3): Better indicators of thyroid function
Laboratory Evaluation:
Hypothyroidism: increased TSH followed by decreased T4, T3
Hyperthyroidism: elevated thyroid hormones with decreased TSH
Page 20: Thyroglobulin as a Tumor Marker
Thyroglobulin Importance: Reflects the presence of thyroid tissue
Post-treatment Surveillance: Ideal marker for thyroid cancer post-surgery and ablation
Testing Methods: RIA, ELISA, IRMA, ICMA
Page 21: Immune Response and Thyroid Antibodies
Role of Autoimmune Processes: Diseases of the thyroid involve antibodies against thyroid tissue
Page 22: TSH Receptor Antibodies
Graves' Disease: Primary cause of hyperthyroidism related to TSH receptor antibodies stimulating hormone production
Page 23: Thyroid Peroxidase Antibodies
Importance in Autoimmune Thyroiditis: Directed against TPO which is crucial for thyroid hormone biosynthesis
Pathophysiological Effects: Inhibition of TPO leads to decreased thyroid hormone production
Page 24: Antibody Test Range for TPO
TPO Antibody Values:
100 IU/ml: Positive
60-100 IU/ml: Equivocal
<60 IU/ml: Negative
Clinical Implications: High antibodies indicate risk for hypothyroidism onset
Page 25: Antithyroglobulin Antibodies
Prevalence: First discovered antibodies against thyroglobulin, frequency increases with age
Page 26: Thyroxine Binding Globulin (TBG)
Function: Acts as a reservoir for T4 in plasma
Clinical Relevance: Little free T3 and T4 available, but those levels are clinically significant
Page 27: Alterations in Binding Proteins
Factors affecting binding: Include pregnancy and hormonal therapies that alter protein levels
Conditions leading to changes: Hypoproteinemic states that reduce binding protein concentrations
Page 28: Parathyroid Hormone (PTH) Effects
Kidneys: PTH increases calcium reabsorption, phosphate excretion, and vitamin D activation
Page 29: Calcium Regulation Mechanism
Role of PTH, Vitamin D, Calcitonin: Mobilize calcium from bones, enhance intestinal absorption, and modulate phosphate excretion
Page 30: Testing for Parathyroid Function
Methods Used: Immunoassays for intact PTH in serum and plasma
Variations in Concentration: Factors in patients with hyperparathyroidism or renal failure
Page 31: Thyroid Ultrasound Advantages
Benefits of High-Resolution US: Non-invasive, cost-effective, and sensitive for thyroid imaging
Guidance for Procedures: Assists in diagnostic and therapeutic interventions
Page 32: Limitations of Ultrasound
Functional Assessment Limitation: Cannot determine thyroid function, requires blood tests for functional status
Characteristic Evaluation: Structural features of nodules provide insight into malignancy but are non-definitive
Page 33: Indications for Thyroid Ultrasound
When to Use: Confirm nodules, assess dimensions and vascularization, identify malignancy, evaluate postoperative status, and guide biopsies
Page 34: Normal Size and Anatomy of Thyroid Gland
Anatomical Details: Two lobes with isthmus—size varies by sex/age
Volume Ranges: 10-15 ml for females, 12-18 ml for males
Page 35: Mixed Composition Nodule Illustration
Image Depiction: Solid/cystic mixed composition of thyroid nodule
Page 36: Immune Thyroiditis Indication
Observation: Diffuse inhomogeneity of left lobe suggests immune thyroiditis
Page 37: Cervical Lymph Node Imaging
Illustration: Thyroid ultrasound depiction of cervical lymph nodes
Page 38: Vascularization Findings
Observation: Amplified diffuse vascularization in thyroid imaging
Page 39: Thyroid Nodules Vascularity
Observation: Increased vascularization patterns around thyroid nodules/masses
Page 40: Innovations in Elastography
US Elastography Explained: Noninvasive method to evaluate thyroid nodule stiffness, helps differentiate benign/malignant nodules
Assessment Techniques: Strain ratio scoring system based on elasticity
Page 41: ELASTOGRAPHY Result for Solid Nodule
Observation: Solid thyroid nodule with rigidity assessment score of 4/5
Page 42: Thyroid Scan and Uptake Overview
Nuclear Medicine Imaging: Noninvasive with radiopharmaceuticals to assess thyroid function and morphology
Page 43: Preparations for Thyroid Studies
Medication Restrictions: No thyroid supplements or iodine-containing solutions before study
Common Radioisotopes Used: Tc-99m and I-131/I-123 for imaging
Page 44: Normal Radionuclide Scan Appearance
Illustration: Displays a normal thyroid during radionuclide scan
Page 45: Nonfunctional Radionuclide Scan Observations
Finding: Nonfunctional thyroid with decreased uptake, no specific image
Page 46: Nonfunctional Nodule Detection
Observation: Imaging reveals nonfunctional left lobe thyroid nodule
Page 47: Hyperfunctional Nodule Imaging
Observation: Hyperfunctional left lobe thyroid nodule identified as adenoma
Page 48: Indication for Parathyroid Imaging
Clinical Use: Detect parathyroid adenoma/hyperplasia in hyperparathyroidism cases
Preferred Radiotracer: Tc-99m sestamibi
Page 49: Combined Imaging Techniques
Differential Washout Examination: Compare washout rates of Tc-99m MIBI between thyroid and abnormal parathyroid tissue
Page 50: Imaging Results for Hyperfunctional Parathyroid
Finding: Indicates hyperfunctional superior left parathyroid adenoma
Page 51: Description of Brown Tumor
Finding in Bone: Geographic lytic lesion in the tibia indicative of a brown tumor due to osteoclastic activity
Page 52: References
Key References:
Michels, T.C., Kelly, K.M. "Parathyroid disorders."
Berne & Levy Physiology, 7th Edition, Koeppen, B.A. Stanton, B.M.
Clinical Chemistry, Bishop, Fody, Schoeff.
Kiess, Hall, Essentials of Anatomy and Physiology.
Ziessman, H.A. NUCLEAR MEDICINE: THE REQUISITES.