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Thursday, August 11, 2016

THYROID GLAND DISORDERS



• GENERAL ASPECTS OF THYROID GLAND


– Anatomy: weight range from 12 to 30g
– Located in the neck, anterior to the trachea
– Produces: T4 & T3 (active hormone)


• Thyroid hormones:

– T4: (Thyroxine) is made exclusively in thyroid gland

• Ratio of T4 to T3 ; 5::1

• Potency of T4 to T3; 1::10

• T4 is the most important source of T3 by peripheral tissue deiodination “ T4 to T3 “

– T3: (Triiodothyronine) main source is peripheral deiodination:

• Ratio of T3 to T4 ; 1::5

• Potency of T3 to T4; 10::1

• T3 is the most important because more than 90% of the thyroid hormones physiological effects are due to the binding of T3 to Thyroid receptors in peripheral tissues.


• PHYSIOLOGY EFFECTS OF THYROID HORMONES

• THEY ARE NOT ESSENTIAL FOR LIFE, BUT ARE EXTREMELY HELPFUL
THYROID GLAND DISORDERS


– Affects every single cell in the body

• Modulates:

– Oxygen consumption

– Growth rate

– Maturation and cell differentiation

– Turnover of Vitamins, Hormones, Proteins, Fat, CHO

• MECHANISMS OF THYROID HORMONE ACTION

– Act by binding to Nuclear receptors, termed Thyroid Hormone Receptors (TRs), Increasing synthesis of proteins

– At mitochondrial level increases number and activity to increasing ATP production

– At Cell membrane increases ions and substrates transmembrane flux


• THYROID HORMONE EFFECTS

– CALORIGENESIS
– GROWTH & MATURATION RATE
– C.N.S. DEVELOPMENT & FUNCTION
– CHO, FAT & PROTEIN METABOLISM
– MUSCLE METABOLISM
– ELECTROLYTE BALANCE
– VITAMIN METABOLISM
– CARDIOVASCULAR SYSTEM
– HEMATOPOIETIC SYSTEM
– GASTROINTESTINAL SYSTEM
– ENDOCRINE SYSTEM
– PREGNANCY



– CALORIGENESIS
• Controls the Basal Metabolic Rate (BMR)

– CHO METABOLISM

• Increases:
– Glucose absorption of the GI tract
– Glucose consumption by peripheral tissues
– Glucose uptake by the cells
– Glycolysis
– Gluconeogenesis
– Insulin secretion



– GROWTH & MATURATION RATE

– C.N.S. DEVELOPMENT & FUNTION

• “ESSENTIAL” in the newborn to prevent development of “CRETINISMS” & to a normal “IQ”

• Modulation of brain cerebration

• Mood modulation


- FAT & PROTEIN METABOLISM

• Increase lipolysis and lipid mobilization with:

– Cholesterol
– Triglicerides
– Free fatty acids

– MUSCLE METABOLISM

• Modulates;

– Strength & velocity of contraction



– ELECTROLYTE BALANCE

• Low Thyroid hormones could induce hyponatremia

– VITAMIN METABOLISM

• Modulates vitamin consumption

– HEMATOPOIETIC SYSTEM

• Could induce anemia


– CARDIOVASCULAR SYSTEM
• Hyperthyroidism, increases:
– Heart rate & myocardial strenght
– Cardiac output
– Peripheral resistances (Vasodilatation)
– Oxygen consumption
– Arterial pressure

• Hypothyroidism, reduces:
– Heart rate & myocardial strenght
– Cardiac output
– Peripheral resistances (Vasodilatation)
– Oxygen consumption
– Arterial pressure

• Modulate bowel movements and absorption

– ENDOCRINE SYSTEM

• Modulates pituitary axis, affecting GH, ACTH, FSH, LH, so-on

– PREGNANCY

• Modulates growth rate and affects lactation
THYROID GLAND DISORDERS
• DIVIDED INTO:

– THYROTOXICOSIS (Hyperthyroidism)
• Overproduction of thyroid hormones

– HYPOTHYROIDISM (Gland destruction)
• Underproduction of thyroid hormones

– NEOPLASTIC PROCESSES
• Beningn
• Malignant

• LABORATORY EVALUATION
TSH normal, practically excludes abnormality

– If TSH is abnormal, next step: Total & Free T4 & T3
- TSI (Thyroid Stimulating Ig)

- TPO (Thyroid Peroxidase Ab)

- Antimitochondrial Ab

- Serum Tg (Thyroglobulin)

- Radioiodine uptake & Thyroid scaning

- FNA, Fine-needle aspiration

- Thyroid ultrasound

• TSH High usually means Hypothyroidism

– Rare causes:
• TSH-secreting pituitary tumor
• Thyroid hormone resistance
• Assay artifact

• TSH low usually indicates Thyrotoxicosis

– Other causes
• First trimester of pregnancy
• After treatment of hyperthyroidism
• Some medications (Esteroids-dopamine)





• THYROTOXICOSIS:
– is defined as the state of thyroid hormone excesss

• HYPERTHYROIDISM:
– is the result of excessive thyroid gland function





• Abnormalities of Thyroid Hormones

– Thyrotoxicosis
• Primary
• Secondary
• Without Hyperthyroidism
• Exogenous or factitious

– Hypothyroidism
• Primary
• Secondary
• Peripheral


• Causes of Thyrotoxicosis:
– Primary Hyperthyroidism
• Grave´s disease
• Toxic Multinodular Goiter
• Toxic adenoma
• Functioning thyroid carcinoma metastases
• Activating mutation of TSH receptor
• Struma ovary
• Drugs: Iodine excess

– Thyrotoxicosis without hyperthyroidism
• Subacute thyroiditis
• Silent thyroiditis
• Other causes of thyroid destruction:
– Amiodarone, radiation, infarction of an adenoma
• Exogenous/Factitia

– Secondary Hyperthyroidism
• TSH-secreting pituitary adenoma
• Thyroid hormone resistance syndrome
• Chorionic Gonadotropin-secreting tumor
• Gestational thyrotoxicosis


• Symptoms:
– Hyperactivity
– Irritability
– Dysphoria
– Heat intolerance & sweating
– Palpitations
– Fatigue & weakness
– Weight loss with increased appetite
– Diarrhea
– Polyuria
– Sexual dysfunction
• Signs:
– Tachycardia
– Atrial fibrillation
– Tremor
– Goiter
– Warm, moist skin
– Muscle weakness, myopathy
– Lid retraction or lag
– Gynecomastia
– * Exophtalmus
– * Pretibial myxedema

• Differential diagnosis:
– Panic attacks

– Psychosis

– Mania

– Pheochromocytoma

– Hypoglycemia

– Occult malignancy

• Treatment:

– Reducing thyroid hormone synthesis:
• Antithyroid drugs (Methimazole, Propylthyouracil)
• Radioiodine (131I)
• Subtotal thyroidectomy

– Reducing Thyroid hormone effects:
• Propranolol
• Glucocorticoids
• Benzodiazepines

– Reducing peripheral conversion of T4 to T3
• Propylthyouracil
• Glucocorticoids
• Iodide (Large oral or IV dosage) (Wolf-Chaikoff effect)

• Treatment: Special considerations:

– Thyrotoxic crisis or Thyroid storm:
• It´s a life-threatening exacervation of thyrotoxicosis, acompanied by fever, delirium, seizures, coma, vomiting, diarrhea, jaundice.
• Mortality rate reachs 30% even with treatment

• It´s usually precipitated by acute illness, such as:

– Stroke, infection,trauma, diabeic ketoacidosis, surgery, radioiodine treatment

• Propylthyouracil IV or Nasogastric tube
• Radioiodine (131I)
• Propranolol
• Glucocorticoids
• Benzodiazepines
• Iodide (Large oral or IV dosage) (Wolf-Chaikoff effect)

• HYPOTHYROIDISM
– Primary

• Autoimmune (Hashimoto´s)
• Iatrogenic Surgery or 131I
• Drugs: amiodarone, lithium
• Congenital (1 in 3000 to 4000)
• Iodine defficiency
• Infiltrative disorders



• Hashimoto´s Thyroiditis or Goitrous thyroiditis
– Mean anual incidence:
• Women 4:1000 Men 1:1000
• Risk factors; TPO antibodies (90%) Japanese, previous history, high I intake
• Average age: 60
• Frequently associated to other autoimmune disorders such as: AR, SLE, Sjogren´s so-on.
• Treatment: Levothyroxine






• CONGENITAL HYPOTHYROIDISM

• Prevalence: 1 in 3000 to 4000 newborns
– Cause: Dysgenesis 85%
– Dx: Blood screning (TSH &/or T4)

• Treatment:
– Supplemental Tx. With Levothyroxine is “essential” for a normal C.N.S. Development and prevention of mental retardation



HYPOTHYROIDISM
– Secondary
• Pituitary gland destruction
• Isolated TSH deficiency
• Bexarotene treatment
• Hypothalamic disorders

– Peripheral:
• Rare, familial tendency


• Symptoms:
– Tiredness
– Weakness
– Dry skin Sexual dysfunction
– Dry skin
– Hair loss
– Difficulty concentrating

• Signs:
– Bradycardia
– Dry coarse skin
– Puffy face, hands and feet
– Diffuse alopecia
– Peripheral edema
– Delayed tendon reflex relaxation
– Carpal tunel syndrome
– Serous cavity effusions.

• SPECIAL TREATMENT CONSIDERATIONS

• Myxedema coma
– Reduced level of consciousness, seizures
– Hypotension/shock
– Hypothermia
– Hyponatremia

• Usually in elderly hypothyroid pts.

• Usually precipitated by intercurrent illnesses that impairs ventilation

• It´s an Emergency with a high mortality rate

• Treatment: Lyotironine(T3) or T4, Hydrocortisone, external warming, IV fluids




• Elderly patients

• Coronary Artery Disease

• Poor adrenal gland reserve

• Childrens

• Pregnancy

• Emergency surgery (Non thyroid related)