Endocrine System

Endocrine System 郑州大学第一附属医院核医学科 Department of NuclearMedicine, FirstAffiliatedHospital, Zhengzhou University

谢新立

Thyroid  Physiology

– Thyroid Hormone Synthesis    

Iodide trapping Organification (iodine and tyrosine) Coupling Proteolysis or Release

– Classification of Thyroid Hormone 





T3(accounts for 10% of thyroid hormone , 99. 5% bound and 0.5% free,more potent) T4(accounts for 90% of thyroid hormone ,99.95% bound and 0.05% free) rT3(inactive)

Thyroid  Physiology – Pertinent Hormone  TRH (synthesized in hypothalamus,can stimulate synthesis and release of thyrotropin)  TSH (synthesized in the pituitary, can stimulate thyroid gland growth and thyroid hormone synthesis)

HYPOTHALAM US TRH PITUITAR Y TS H

﹢

-10% FT3

I99m TcO4

T3-TBG 99.5% 90% FT4 T4-TBG 99.95%

I-→ I → Hormone Synthesis

In Vivo Thyroid Function Tests RAIU(Radioactive Iodine Uptake Test) 

Thyroid uptake determination is the measurement of the fraction of an administered amount of radioactive iodine that accumulates in the thyroid at selected times following ingestion.

 Common

Indications

– To confirm hyperthyroidism and determine the cause of

thyrotoxicosis – Assist in determining the amount of 131I to be administered to patients for therapy of hyperthyroidism or for ablation of thyroid remnants – RAIU is of limited value in diagnosing hypothyroidism

In Vivo Thyroid Function Tests  Procedure – Patient preparation  Avoidance of interfering materials – medications such as thyroid hormones and antithyroid drugs, – Iodine containing food such as kelp and lobster – Medications such as iodiated contrast, amiodarone ,betadine 

Empty stomach

In Vivo Thyroid Function Tests  Radiophamaceutical – 131I : 5~10 uCi – 123I :200~300 uCi

 Data

acquisition

– Instumentation (an probe) – Measurement of uptake

 Processing – %uptake=[(neck counts － net thigh counts) ×100] ÷(net

standard counts)

In Vivo Thyroid Function Tests  Clinical

interpretation

– Normal range  4h: 6~18%  24h: 10~35%

The RAIU test provides a useful assessment of thyroid function: in general ,the higher the iodine uptake,the more active the gland.

In Vivo Thyroid Function Tests  Etiologies

resulting in an increased RAIU

– Hyperthyroidism – Rebounding following abrupt withdrawal of antithyroid – – – – – –

drugs Long term antithytoid therapy Enzyme defects Iodine starvation Lithium therapy Eraly hashimoto’s thyroiditis Rebound during recovery from subacute thyroiditis

In Vivo Thyroid Function Tests  Etiologies

resulting in a decreased RAIU

– Blocked trapping   

Iodine load Exogenous thyroid hormone replacement depressing TSH levels Ectopic thyroid : Struma Ovarii

– Blocked organification – Parenchymal destruction – Hypothyroidism  

Primary and secondary Surgical / radioiodine ablation of thyroid

In Vitro Thyroid Function Tests  TT3 – Bounded T3 – Unbounded T3 (FT3)

 TT4 – Bounded T4 – Unbounded T4 (FT4)

 TSH

Thyroid Scintigraphy Common Indications  



  

To relate the general structure of the thyroid gland to its function(such as nodular or diffuse enlargement) To correlate thyroid palpation with scintigraphic findings to determine whether the degree of function in a clinically defined area or nodule To locate ectopic thyroid tissue or determine whether a suspected “thyroglossal duct cyst” is the only functioning thyroid tissue present To assist in evaluation of congenital hypothyroidism To evaluate a neck or substernal mass To differentiate thyroiditis and factitious hyperthyroidism from Grave’s disease and other form of hyperthyroidism

Thyroid Scintigraphy radiopharmaceuticals   I-123 I-131 Tc-99m

  

Administrtion po po po iv

dose 200-400μCi 25~100μCi 5 mCi 3 mCi

Imaging time 3~4h 16~24h 1h 15~30min

Imaging the Thyroid normal appearances The normal thyroid image is variable. Commonly, the lobes are asymmetrical and the isthmus is not always fully visible.

Thyroid Scintigraphy  Clinical

applications

– Ectopic thyroid tissue  Lingual thyroid  Thyroglossal duct cyst  Substernal thyroid  Stuma ovarii

Thyroid Scintigraphy Clinical Application  thyroid nodules

“hot nodule” :has greater or more radioactivity than the normal surrounding thyroid tissue, Benign Autonomous (50%) Adenomatous hyperplasia Compensatory hypertrophy Physiologic thyroid hyperplasia

Malignant Thyroid carcinoma (less than 4%)

Thyroid Scintigraphy Clinical Application  thyroid nodules “cold nodule” : has less activity than the normal surrounding thyroid tissue, Benign (80~85%) Simple cyst Adenomatous hyperplasia Focal hemorrhage Inflammatory Parathyroid adenoma

Malignant(20%) Thyroid carcinoma Parathyroid adenoma/ carcinoma Thyroid lymphoma Metastatic disease

Thyroid Scintigraphy Clinical Application  thyroid nodules “indeterminate nodule” : has activity equal to the adjacent thyroid gland A thyroid suppression test may be performed to determine if the nodule is autonomous or cold . Cold nodules require further evaluation to exclude malignancy.

Thyroid Scintigraphy  Clinical

Application

– Congenital lesions of the thyroid gland – Iodine deficiency goiter – Thyrotoxicosis  

Grave’s disease Toxic nodular goiter

– Thyroiditis    

Acute Subacute Silent Chronic lymphocytic thyroiditis

Extended scintigraphy for differentiated thyroid cancr  Radiophamacerticals – 131I or 123I – 201TL – 99mTc-MIBI

Extended scintigraphy for differentiated thyroid cancr  Patient

preparation

Diffuse Toxic Goiter (Graves Disease) Graves' disease is an autoimmune disorder characterized by the presence of a TSH receptor antibody.

Clinical Findings The age of onset is most commonly between 30-40 years. Females are much more commonly affected than men (7:1). Patients present with a goiter, exophthalmos, tachycardia, weight loss, heat intolerance, hyperactive reflexes, warm skin, lid lag, and/or a tremor. The thyroid gland may be normal sized in a small number of patients.

Clinical Findings T3 and T4 levels are elevated and TSH is decreased in patients with Graves disease. T3 levels are typically three times normal, while T4 values are usually double. Early in the disease, only T3 toxicosis may be seen.

Imaging Scintigraphy with either I-123 or Tc04 is useful in excluding other causes of thyrotoxicosis. The scan generally demonstrates a uniform distribution of increased activity in an enlarged gland, with decreased background activity .

RAIU An elevated RAIU. If iodide turnover is rapid, early RAIU values will be markedly elevated, but may be normal by 24 hours.

Treatment for Graves disease 

Surgery Sufficient thyroid tissue is removed to reduce overall hormone output.

Treatment for Graves disease 

Antithyroidal drugs Antithyroid drugs such as the thionamides Propylthiouracil and Tapazole (Methimazole) act by blocking the intrathyroidal organification (iodination) of the tyrosine residues on the thyroglobulin molecule by interacting with the enzyme thyroid peroxidase- thereby inhibiting thyroid hormone formation.

Treatment for Graves disease 

I-131 Therapy for Hyperthyroidism  Technique

I-131 is the treatment of choice for patients over the age of 30, or those with medical complications of their thyroid disease. The dose of I-131 is approximately 80-200 uCi per gram of thyroid.

Treatment for Graves disease  I-131

Therapy for Hyperthyroidism

Dose Determination: Dose= (Thyroid mass[gms] x 80-200 uCi/gm)/ Percent uptake

 Amiodarone

英文释义 An antianginal and antiarrhythmic drug. It increases the duration of ventricular and atrial muscle action by inhibiting Na,Kactivated myocardial adenosine triphosphatase. There is a resulting decrease in heart rate and in vascular resistance.

 Struma

Ovarii 英文释义 A rare teratoid tumor of the ovary composed almost entirely of thyroid tissue, with large follicles containing abundant colloid. Occasionally there are symptoms of hyperthyroidism. 5-10% of struma ovarii become malignant, the only absolute criterion for which is the presence of metastasis. (Dorland, 27th ed; Segen, Dictionary of Modern Medicine, 1992)

 Propylthiouracil

英文释义 A thiourea antithyroid agent. Propythiouracil inhibits the synthesis of thyroxine and inhibits the peripheral conversion of throxine to triiodothyronine. It is used in the treatment of hyperthyroidism. (From Martindale, The Extra Pharmacopeoia, 30th ed, p534)

 Myxedema

英文释义 A condition characterized by a dry, waxy type of swelling with abnormal deposits of mucin in the skin and other tissues. It is produced by a functional insufficiency of the thyroid gland, resulting in deficiency of thyroid hormone. The skin becomes puffy around the eyes and on the cheeks and the face is dull and expressionless with thickened nose and lips. The congenital form of the disease is CRETINISM.