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THYROID DISORDERS

THYROID DISORDERS. Abdelaziz Elamin. MD, PhD, FRCPCH Professor of Child Health Consultant Pediatric Endocrinologist Sultan Qaboos University, Oman. HYPOTHYROIDISM-EPIDEMIOLOGY. Neonatal screening reveals incidence that varies between 1-5/1000 live births

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THYROID DISORDERS

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  1. THYROID DISORDERS Abdelaziz Elamin. MD, PhD, FRCPCH Professor of Child Health Consultant Pediatric Endocrinologist Sultan Qaboos University, Oman

  2. HYPOTHYROIDISM-EPIDEMIOLOGY • Neonatal screening reveals incidence that varies between 1-5/1000 live births • The most common cause of preventable mental retardation in children • Both acquired & congenital forms are linked to iodine deficiency • Diagnosis is easy & early treatment is beneficial

  3. ETIOLOGY • CONGENITAL • Hypoplasia & mal-descent • Familial enzyme defects • Iodine deficiency (endemic cretinism) • Intake of goitrogens during pregnancy • Pituitary defects • Idiopathic

  4. ETIOLOGY /2 • ACQUIRED • Iodine deficiency • Auto-immune thyroiditis • Thyroidectomy or RAI therapy • TSH or TRH deficiency • Medications (iodide & Cobalt) • Idiopathic

  5. KILPATRIK GRADING OF GOITRE • Grade 0: Not visible neck extended & Not palpable • Grade 1: Not visible, but palpable • Grade 2: Visible only when neck is extended & on swallowing, • Grade 3: Visible in all positions • Grade 4: Large goiter

  6. THYROID GLAND • Derived from pharyngeal endoderm at 4/40 • Migrate from base of the tongue to cover the 2&3 tracheal rings. • Blood supply from ext. carotid & subclavian and blood flow is twice renal blood flow/g tissue. • Starts producing thyroxin at 14/40.

  7. OVERVIEW (2) • Maternal & fetal glands are independent with little transplacental transfer of T4. • TSH doesn’t cross the placenta. • Fetal brain converts T4 to T3 efficiently. • Average intake of iodine is 500 mg/day. 70% of this is trapped by the gland against a concentration gradient up to 600:1

  8. THYROID HORMONES • Iodine & tyrosine form both T3 & T4 under TSH stimulation. However, 10% of T4 production is autonomous and is present in patients with central hypothyroidism. • When released into circulation T4 binds to: • Globulin TBG 75% • Prealbumin TBPA 20% • Albumin TBA 5%

  9. THYROID HORMONES (2) • Less than 1% of T4 & T3 is free in plasma. • T4 is deiodinated in the tissues to either T3 (active) or reverse T3 (inactive). • At birth T4 level approximates maternal level but increases rapidly during the first week of life. • High TSH in the first 5 days of life can give false positive neonatal screening

  10. TSH • Is a Glico-protein with Molecular Wt of 28000 • Secreted by the anterior pituitary under influence of TRH • It stimulates iodine trapping, oxidation, organification, coupling and proteolysis of T4 & T3 • It also has trophic effect on thyroid gland

  11. TSH (2) • T4 & T3 are feed-back regulators of TSH • TSH is stimulated by a-adrenergic agonists • TSH secretion is inhibited by: • Dopamine • Bromocreptine • Somatostatin • Corticosteroids

  12. THYROID HORMONES (3) • Conversion of T4 to T3 is decreased by: • Acute & chronic illnesses • b-adrenergic receptor blockers • Starvation & severe PEM • Corticosteroids • Propylthiouracil • High iodine intake (Wolff-Chaikoff effect)

  13. THYROXINE (T4) • Total T4 level is decreased in: • Premature infants • Hypopituitarism • Nephrotic syndrome • Liver cirrhosis • PEM • Protein losing entropathy

  14. THYROXINE (2) • Total T4 is decreased when the following drugs are used: • Steroids • Phenytoin • Salicylates • Sulfonamides • Testosterone • Maternal TBII

  15. THYROXINE (3) • Total T4 is increased with: • Acute thyroiditis • Acute hepatitis • Estrogen therapy • Clofibrate • iodides • Pregnancy • Maternal TSI

  16. FUNCTIONS OF THYROXINE • Thyroid hormones are essential for: • Linear growth & pubertal development • Normal brain development & function • Energy production • Calcium mobilization from bone • Increasing sensitivity of b-adrenergic receptors to catecholeamines

  17. CLINICAL FEATURES • Gestational age > 42 weeks • Birth weight > 4 kg • Open posterior fontanel • Nasal stuffiness & discharge • Macroglossia • Constipation & abdominal distension • Feeding problems & vomiting

  18. CLINICAL FEATURES (2) • Non pitting edema of lower limbs & feet • Coarse features • Umbilical hernia • Hoarseness of voice • Anemia • Decreased physical activity • Prolonged (>2/52) neonatal jaundice

  19. CLINICAL FEATURES (3) • Dry, pale & mottled skin • Low hair line & dry, scanty hair • Hypothermia & peripheral cyanosis • Hypercarotenemia • Growth failure • Retarded bone age • Stumpy fingers & broad hands

  20. CLINICAL FEATURES (5) • Skeletal abnormalities: • Infantile proportions • Hip & knee flexion • Exaggerated lumbar lordosis • Delayed teeth eruption • Under developed mandible • Delayed closure of anterior fontanel

  21. OCCASIONAL FEATURES • Overt obesity • Myopathy & rheumatic pains • Speech disorder • Impaired night vision • Sleep apnea (central & obstructive) • Anasarca • Achlorhydria & low intrinsic factor

  22. OCCASIONAL FEATURES (2) • Decreased bone turnover • Decreased VIII, IX & platelets adhesion • Decreased GFR & hyponatremia • Hypertension • Increased levels of CK, LDH & AST • Abnormal EEG & high CSF protein • Psychiatric manifestations

  23. ASSOCIATIONS • Autoimmune diseases (Diabetes Mellitus) • Cardiomyopathy & CHD • Galactorrhoea • Muscular dystrophy + pseudohypertrophy (Kocher-Debre-Semelaigne)

  24. GOITROGENS • DRUGS • Anti-thyroid • Cough medicines • Sulfonamides • Lithium • Phenylbutazone • PAS • Oral hypoglycemic agents

  25. GOITROGENS • FOOD • Soybeans • Millet • Cassava • Cabbage

  26. CLINICAL FEATURES (4) • Neurological manifestations • Hypotonia & later spasticity • Lethargy • Ataxia • Deafness + Mutism • Mental retardation • Slow relaxation of deep tendon jerks

  27. CONGENITAL HYPOTHYRODISM • Primary thyroid defect: usually associated with goiter. • Secondary to hypothalamic or pituitary lesions: not associated with goiter. • 2 distinct types of presentation: • Neurological with MR-deafness & ataxia • Myxodematous with dwarfism & dysmorphism

  28. DIAGNOSIS • Early detection by neonatal screening • High index of suspicion in all infants with increased risk • Overt clinical presentation • Confirm diagnosis by appropriate lab and radiological tests

  29. LABROTARY FINDINGS • Low (T4, RI uptake & T3 resin uptake) • High TSH in primary hypothyroidism • High serum cholesterol & carotene levels • Anaemia (normo, micro or macrocytic) • High urinary creatinine/hydroxyproline ratio • CXR: cardiomegaly • ECG: low voltage & bradycardia

  30. IMAGING TESTS • X-ray films can show: • Delayed bone age or epiphyseal dysgenesis • Anterior peaking of vertebrae • Coxavara & coxa plana • Thyroid radio-isotope scan • Thyroid ultrasound • CT or MRI

  31. TREATMENT (2) • L-Thyroxin is the drug of choice. Start with small dose to avoid cardiac strain. • Dose is 10 mg/kg/day in infancy. In older children start with 25 mg/day and increase by 25 mg every 2 weeks till required dose. • Monitor clinical progress & hormones level

  32. TREATMENT • Life-long replacement therapy • 5 types of preparations are available: • L-thyroxin (T4) • Triiodothyronine (T3) • Synthetic mixture T4/T3 in 4:1 ratio • Desiccated thyroid (38mg T4 & 9mg T3/grain) • Thyroglobulin (36mg T4 & 12mg T3/grain)

  33. THYROID FUNCTION TESTS 1.Peripheral effects: • BMR • Deep Tendon Reflex • Cardiovascular indices (pulse, BP, LV function tests) • Serum parameters (high cholesterol, CK, AST, LDH & carcino-embryonic antigen)

  34. THYROID FUNCTION TESTS (2) 2. Thyroid gland economy: • Radio iodine uptake • Perchlorate discharge test (+ve in Pendred syndrome & autoimmune thyroiditis) • TSH level • TRH stimulation tests • Thyroid scan

  35. THYROID FUNCTION TESTS (3) 3. Tests for thyroid hormone: • Total & free T4 & T3 • Reverse T3 level • T3 Resin Uptake • T3RU x total T4= Thyroid Hormone Binding Index (formerly Free Thyroxin Index)

  36. THYROID FUNCTION TESTS (4) • Special Tests: • Thyroglobulin level • Thyroid Stimulating Immunoglobulin • Thyroid antibodies • Thyroid radio-isotope scan • Thyroid ultrasound • CT & MRI • Thyroid biopsy

  37. PROGNOSIS • Depends on: • Early diagnosis • Proper diabetes education • Strict diabetic control • Careful monitoring • Compliance

  38. MYXOEDMATOUS COMA • Impaired sensorium, hypoventilation bradycardia, hypotension & hypothermia • Precipitated by: • Infections • Trauma (including surgery) • Exposure to cold • Cardio-vascular problems • Drugs

  39. PROGNOSIS • Is good for linear growth & physical features even if treatment is delayed, but for mental and intellectual development early treatment is crucial. • Sometimes early treatment may fail to prevent mental subnormality due to severe intra-uterine deficiency of thyroid hormones

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