2. HYPOTHALAMIC / PITUITARY THYROID AXIS
TRH: stimulate anterior pituitary to release TSH.
TSH: stimulate thyroid for synthesis and release of T4 and T3.
Low T4, Low T3: stimulate TSH and TRH
High T4, High T3: inhibit TSH and TRH
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3. THYROID HORMONES
T4 to T3 secretion ratio - 10:1
T3 is 4X more biologically active than T4
T1/2: T4 = 7days, T3 = 1 day
Both T4 & T3: >99% bound to protein, i.e. metabolically inactive
From thyroid:
100% of the T4
20% of the T3
Remainder of T3 is from peripheral conversion of T4 to T3
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4. Thyroid testing
Biochemical
TSH - highly sensitive
- best test for thyroid function.
Free T4 (FT4) - biologically active
Free T3 (FT3) - biologically active
- FT3 is rarely need to check unless TSH is low or undetectable
with a normal FT4
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5. Functional Disorders of the thyroid Gland
Primary Vs secondary/tertiary
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Primary - disorders resulting from the pathologies of thyroid gland itself
Secondary – thyroid disorders resulting from pituitary gland abnormalities
Tertiary - disorder resulting from hypothalamic pathologies
6. Specific thyroid abnormalities
• Hypothyroidism
• Hyperthyroidism
• Thyroiditis
• Thyroid enlargement
– Diffuse or multiple nodular
Goiter
– Solitary nodules
• Cold
• Warm or Hot
– Cysts
– Malignancies
Functional / Biochemical Structural / Anatomy
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8. Hypothyroidism ……….
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Primary
Goiterous
Non-goiterous
Secondary/tertiary
- From various insults to the pituitary
and hypothalamus
9. Primary hypothyroidism
• Identification on clinical basis can be challenging
• Symptoms are generally vague
• Insidious onset + poor index of suspicion leading to misdiagnosis
• Frequently goes unnoticed, confused as other health problems
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10. Etiology of primary hypothyroidism
Autoimmune: the most common cause
- Chronic lymphocytic thyroiditis = Hashimoto’s
Iatrogenic:
- Radio active iodine Rx, total/subtotal thyroidectomy, neck irradiation
Iodine deficiency
Congenital:
- Thyroid agenesis, dysgenesis, biochemical defect
Drug induced:
- Lithium, amiodarone, chemotherapy, others
Others : Subacute thyroiditis
Peripheral tissue hormone insensitivity (resistance)
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C/F:- Signs & symptoms relates to
hypo-metabolism - BMR
(almost every organ/system
involved)
Symptoms and signs
Weakness & lethargy
Sleepiness
Fatigue, slow speech & thinking
Cold intolerance
Puffy appearance
Constipation
↓ appetite but Wt gain
Irregular and heavy menses
Hoarseness of voice
o Non-pitting edema + puffiness
Myxedema
o Hypothermia
o Macroglosia
o Goiter
o Hypoventilation, pleural
effusion
o ↓ PR, pericardial effusion (↓
CO)
o Dry coarse skin & hair, hair
loss
o Signs of anemia (NC, NC)
o “hang-up” reflex (DTR)
o Psychiatric features (e.g.
depression)
o Cretinism (if severe & in
infancy)
o Myxedema coma
13. Treatment hypothyroidism
• Levothyroxine (LT4)
• Lifelong treatment in most cases
• Check TSH no sooner than 6 weeks after initial start of LT4 or any
adjustment
• Annually once an euthyroid state is established
• Start at low dose in
- Elderly patients or any patient 50 years of age or with underlying
cardiac disease
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14. II. THYROTOXICOSIS/HYPERTHYROIDISM
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Etiology of thyrotoxicosis:
- Diffuse toxic goiter (Graves’ disease)
The most common cause
Autoimmune
F > M, most females b/n age 20 & 50
- Nodular toxic goiter – Solitary or multi nodular
- Usually older Patients
- Sub acute thyroiditis
- Factitious/ iatrogenic
- Rare forms : TSH e.g. pituitary (20 or 30) , ovarian tumor
Excess Iodine ingestions.
15. Common Symptoms and Signs of Thyrotoxicosis
Symptoms
• Nervousness / behavioral changes
• restlessness
• Fatigue, weight loss
• Muscle weakness
• Increased perspiration
• Heat intolerance
• Tremor
• Palpitations
• Appetite/weight changes, diarrhea
Menstrual disturbances
(oligomenorrhea / amenorrhea)
Signs
• Goiter +/- bruit
• Hyperactivity
• Tachycardia / arrhythmia
• Systolic hypertension
• Warm, moist, or smooth skin
• Stare and eyelid retraction
• Tremor
• Hyper-reflexia
• Pre-tibial myxoedema
• Clubbing (Acropathy)
• Exophthalmos
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16. Tedla K, the thyroid gland, August 2015 16
Thyroid Storm
- Is the most severe form of thyrotoxicosis
- Is a medical emergency
- Attended by high mortality
- Diagnosis is clinical
17. Thyrotoxicosis - work-up
Lab tests
• TSH - Low or undetectable
• Free T4 and/or Free T3 – Increased
radio isotop thyroid scan / uptake
• Uptake is increased
• Increased radiotracer uptake
– Homogeneous ( Graves’ disease)
– multiple areas (Toxic MNG)
– single area (Hot or warm nodule)
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18. Treatment Options for Thyrotoxicosis
• I131 RAI thyroid ablation
• Anti-Thyroid Drugs (ATD’s)
– Methimazole
– Propylthiouracil (PTU)
• Surgery: very rarely indicated
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- Is an inflamation of the thyroid gland
Types:
1. Subacute (granulomatous or de Quervian’s)
2. Chronic thyroiditis (Hashimoto’s):
3. Chronic thyroiditis with transient thyrotoxicosis
THYROIDITIS
