Thyroid Function Tests Orishaba Diana And Enoch T

Introduction to the Thyroid Gland Objectives Explain the synthesis and regulation of thyroid hormone production Describe the actions of thyroid hormones Describe the etiology, major symptoms and pathophysiology of hyper and hypothyrodism Understand the role of thyroid hormone measurement in the management of thyroid disease

Control of thyroid hormone production Peripheral tissues

Metabolic Effects of Thyroid Hormones Effects on the function of virtually every organ system Maintain metabolic stability and increase resting or basal metabolic rate Increase heart rate Increase mental alertness Maintain GI motility & bone turnover Brain dev’t and skeletal maturation during foetal development

Thyroid hormones regulate: -Growth and development -Temperature -Oxygen consumption -Metabolism of carbohydrate, protein and lipid -TSH secretion

Thyroid disease Can be Hypothyroidism or Hyperthyroidism. Either way, this can be a primary disease of the thyroid gland or secondary to brain lesions. TFTs alone can differentiate the above. Other Ix are important for specific causes eg Anti-thyroid antibodies (Anti-peroxidase) –in hashimoto’s thyroiditis, titre tells likelihood of progression to overt hypothyroidism. TSH receptor antibodies – Grave’s CT scan in brain lesions Radio iodine nuclide studies etc NB: Goitre refers to thyroid swelling and can be both in patients with hypothyroidism, euthyroidism or hyperthyroidisim.

Primary Causes Autoimmune (Hashimoto’s) Thyroiditis Congenital hypothyroidism Thyroiditis Post surgery Irradiation (Radioactive iodine, Head & Neck Ca) Dietary Iodine deficiency Drug effects including anti- thyroid medication High amounts of Iodine eg Amiodarone Thyroid gland agenesis/dysgenesis Infiltrations – Amyloidosis, Haemochromatosis, Fibrous Thyroiditis (Reidel’s) Subacute (Viral), Painless (Postpartum) Thyroiditis: Transient Hypothyroidism HYPOTHYROIDISM Low T3 and/or T4

Other Findings Anaemia Hyponatremia Elevated triglycerides & Cholesterol Sinus bradycardia Pericardial effusion ECG: Low voltage Slow relaxation of deep tendon reflexes

Diagnosing Hypothyroidism Insidious onset, so recognition is sometimes difficult. Always remember the Negative Feedback Loop: TSHFree T4/T3Diagnosis ↑↓Overt Primary Hypothyroidism ↑→ (usually low normal) Subclinical Primary Hypothyroidism ↓↓Secondary Hypothyroidism

Major Causes of Hyperthyroidism Graves disease Toxic multinodular goitre Toxic nodule Thyroiditis Excess replacement TSH secreting tumour Amiodarone Ectopic thyroid tissue Trophoblasctic tumours HYPERTHYROIDISM Raised T3 and/or T4

Other Findings Increased appetite Weight loss Resting tremor Wide pulse pressure Flow murmur Proximal muscle weakness Brisk deep tendon reflexes

Diagnosing Hyperthyroidism Try to identify the underlying cause, because treatments vary Use Hx, physical exam, Imaging, antibody tests, etc Always remember the negative feedback loop TSHFree T4/T3Diagnosis ↓↑Overt primary hyperthyroidism ↓→Subclinical primary hyperthyroidism ↑↑Secondary hyperthyroidism

TSH ( mU/L) Free T 4 (10-25 pmol/L) Free T 3 ( pmol/L)

Patient A Clinical Biochemistry Sample collected : XX-Aug-XX Ref. Range Serum T.S.H <0.1 mIU/L ( 0.3 – 3.5 ) Free T pmol/L ( ) Free T pmol/L ( ) 1.Patient comes with weight loss and palpitations. Below is his thyroid panel. What is your specific diagnosis? Some Questions

Patient A Clinical Biochemistry Sample collected : XX-Aug-XX Ref. Range Serum T.S.H mIU/L ( 0.3 – 3.5 ) Free T pmol/L ( ) Free T pmol/L ( ) 2. Clinical information – Cold intolerance, constipation What is your specific diagnosis?

Hypothyroidism Treatment Depending on the cause but usually is thyroid replacement using Levo thyroxine

Hyperthyroidism Rx 1. Beta Blockers Sympathomimetic blockers Propranolol also inhibits peripheral conversion of T4 to T3 Sole Tx in transient thyrotoxicosis 2. Antithyroid drugs: Thionamides eg CARBIMAZOLE Inhibit thyroid hormone synthesis Can induce remission in Grave’s disease Control thyrotoxicosis before radioiodine or surgery In Grave’s: Keep on drugs for months, then taper to see if there’s remission S/Es: Rash, Pruritus, Arthralgias, Agranulocytosis Pregnancy: Potassium ThioUracil(PTU)

Hyperthyroidism Rx 3. RadioActive Iodine Oral Concentrates in the thyroid gland Localised destruction Postablative hypothyroidism 4. Surgery Toxic Adenoma: Lobectomy Toxic MNG with compressive symptoms KI/Lugol’s solution Reduces vascularity pre- surgery

Conclusion Interpretation of TFT’s TSHT4T3 Primary hypothyroisism Highlow Secondary hypothyroidism low Primary hyperthyroidism Lowhigh Secondary hyperthyroidism high