THYROID DYSFUNCTION Dr. Hany Ahmed Assistant Professor of Physiology (MD, PhD). Al Maarefa Colleges (KSA) & Zagazig University (ARE) Specialist of Diabetes, Metabolism and Obesity Zagazig Obesity Management & Research Unit

Objectives The student should be able to: Describe the etiology, symptoms and treatment of thyrotoxicosis. Describe the etiology, symptoms and treatment of hypothyroidism.

DISORDERS OF THYROID FUNCTION Hypothyroidism: - Deficient thyroid hormone secretion. Hyperthyroidism: - Excess thyroid hormone secretion.

Hypothyroidism Deficient thyroid hormones secretion: In infants & children: Cretinism In adults: Myxedema

Hypothyroidism Causes: Primary failure of thyroid gland itself. Secondary to deficiency of TRH or TSH or both. Inadequate dietary supply of iodine.

1- Cretinism Hypothyroidism in utero or early life Causes: 1- Complete absence of thyroid gland. 2- Metabolic defect (the gland is unable to make hormones). Clinical picture: The defect is usually detected at 6 months of age. - The infant is Idiot (mentally retarded) with coarse facies. - Short child with short limbs. - Dry skin, scanty hair & Large protruding tongue & open mouth. - Depressed nose due to delayed bone growth. - Delayed teeth eruption, defective speech & hoarsy cry. - Weak abdominal wall, bulging abdomen and umbilical hernia.

- Delayed walking, sitting , Incontinent to urine & stool. - Hypothermia (↓ BMR) & ↑ Serum cholesterol. - Hypogonadism Treatment: Thyroxin for life (as early as possible).

Cretinism & Dwarfism

2- MYXEDEMA Hypothyroidism in adults due to: 1- Damage of thyroid tissue (autoimmune disorder). 2- After unavoidable surgical removal. 3- Metabolic defect. C/P: A reduction in overall metabolic activity & Reduced BMR. Displays poor tolerance of cold. Dry cold skin. Puffy appearance of face. Tendency to gain excessive weight. Easily fatigued (lower energy production). Appetite loss & constipation.

MYXEDEMA 8) Slow and weak pulse (caused by a reduction in the rate and strength of cardiac contraction and a lowered cardiac output). 9) Slow reflexes, slow mental responsiveness, diminished alertness, slow speech, sleepiness and poor memory. 10) Hair loss in head and outer of eye brow (vitamin A deficiency). 11) Arteriolosclerosis ( Serum cholesterol). 12) Accumulation of muco-proteins & fluids in subcutaneous tissues  non pitting edema. 13) Anemia. Treatment: – If diagnosed early, can be treated by administrating of T4 – Hypothyroidism caused by iodine deficiency; treated by dietary iodine.

HYPERTHYROIDISM The most common cause of hyperthyroidism is Graves’ disease. Autoimmune disease  Excessive production of thyroid hormones due to presence of some antibodies (LATS = Long Acting Thyroid Stimulator or thyroid-stimulating immunoglobulin (TSI). C/P: Eye: Exophthalmos: protrusion of eye ball. Due to deposition of fat and edema behind eye ball. It is associated with lid retraction, pupillary dilatation, congestion and oedema

Thyrotoxicosis Effects of excess thyroxin:  BMR & O2 consumption  sensitivity to heat. Loss of weight in spite of  appetite &  GIT motility  diarrhea. ↑ Protein catabolism  muscle weakness. Mobilization of fat & ↓ blood cholesterol level. ↑ Blood glucose with mild glycosuria. Demineralization of bones ↑ Ca++ and P04 excretion in urine. ↑ Nervous excitability (fine tremors of outstretched hands & insomnia). ↑ Heart rate, COP, ABP & water hammer pulse  heart failure.

Thyrotoxicosis Sympathetic potentiation: Due to  number & affinity of receptors to catecholamine. Tachycardia, sweating, tremors, anxiety.

Role of thyroid-stimulating immunoglobulin in Graves’ disease: Thyroid-stimulating immunoglobulin (TSI), an antibody erroneously produced in the autoimmune condition of Graves’ disease, binds with TSH receptors on thyroid gland and continuously stimulates thyroid hormone secretion outside the normal -ve feedback control system.

Treatment of thyrotoxicosis Anti-thyroid Drugs: Carbimazol is drug of choice. Subtotal surgical removal: The gland must be controlled before operation; iodine is given for 7 days to diminish vascularity and size (Wolff-Chaikoff effect). Destruction by irradiation: Iodine I131 is used.

GOITER Goiter is an enlargement of thyroid gland. Simple goiter: due to deficiency of iodine supply   thyroid hormones formation   TSH   thyroid growth. Exophthalmic goiter: Occurs when TSI excessively stimulates the thyroid gland. Goiter with hypofunction.

References Human physiology, Lauralee Sherwood, seventh edition. Text book physiology by Guyton &Hall,11th edition. Text book of physiology by Linda .S .Costanzo third edition