Thyroid lecture 2023

1. Thyroid Gland
Dr.Sama Atta

5. • T4 can be regarded as a prohormone, since it has a longer half-life in blood than T3
(approximately 1 week compared with approximately 18 hours), and binds and activates thyroid
hormone receptors less effectively than T3. T3 and T4 circulate in plasma almost entirely bound to
thyroxine-binding globulin (TBG). TBG levels are increased by oestrogen (such as in the combined
oral contraceptive pill) and this will result in raised total T3 and T4, although free thyroid hormone
levels are normal.

7. Thyrotoxicosis
• Symptoms
• 1)weight loss with a normal or increased appetite,hyperdefecation
• 2) heat intolerance
• 3)palpitations
• 4)tremor
• 5) irritability, emotional lability,anxiety
• 6)sweating

8. • Common signs:
• 1) Tachycardia, Atrial fibrillation occurs in about 10% of patients with thyrotoxicosis.
• 2) Muscle weakness , Periodic paralysis
• 3)Osteoporosis (fracture, loss of height)
• 4)Anxiety, psychosis
• 5)Pruritus, alopecia
• 6)Amenorrhea/oligomenorrhoea
• 7) palmar erythema
• 8) lid retraction and lid lag, due to potentiation of sympathetic innervation of the levator palpebrae muscles,
• 9) Not all patients have a palpable goitre.

9. Causes of thyrotoxicosis
• 1) Graves disease 75%
• It is an autoimmune thyroid disease, The thyrotoxicosis results from the production of antibodies
directed against the TSH receptor on the thyroid follicular cell, TSH receptor antibodies (TRAb)
which stimulate thyroid hormone production and proliferation of follicular cells.
• characterized by triad of : Exophthalmos, Diffuse goite ( with bruits) and pretibial myxedema.

13. 2) subacute (de Quervain’s) thyroiditis
• It is a transient inflammation of the thyroid gland occurring after infection with Coxsackie, mumps
or adenoviruses. There is pain in the region of the thyroid that may radiate to the angle of the jaw
and the ears, and is made worse by swallowing, coughing and movement of the neck. The thyroid
is usually palpably enlarged and tender.
•
• inflammation in the thyroid gland is associated with release of stored thyroid hormones. As a
result, T4 and T3 levels are raised for 4–6 weeks until the pre-formed colloid is depleted.
Thereafter, there is usually a period of hypothyroidism of variable severity before the follicular
cells recover and normal thyroid function is restored within 4–6 months .

14. • In the thyrotoxic phase, the iodine uptake is low because the damaged follicular cells are unable
to trap iodine ,erythrocyte sedimentation rate (ESR) is usually raised.
• Treatment measures include :NSAIDs, β-blocker, prednisolone 40 mg daily for 3–4 weeks may be
used .Antithyroid drugs are of no benefit because thyroid hormone synthesis is impaired rather
than enhanced. Careful monitoring of thyroid function and symptoms is required so that
levothyroxine can be prescribed temporarily in the hypothyroid phase.

15. 3) Postpartum thyroiditis
• symptomatic thyrotoxicosis presenting for the first time within 12 months of childbirth is likely to
be due to post-partum thyroiditis and the diagnosis is confirmed by low radio-isotope uptake .
Post-partum thyroiditis tends to recur after subsequent pregnancies, and eventually patients
progress over a period of years to permanent hypothyroidism.

16. 4)Toxic adenoma

18. 5) Toxic multinodular goitre

19. 6) Thyroid carcinoma
• Papillary carcinoma: This is the most common of the malignant thyroid tumours and accounts for 90%
of radiation-induced thyroid cancer. spread is initially to cervical lymph nodes.
• Follicular carcinoma : This is usually a single encapsulated lesion. Spread to cervical lymph nodes is rare.
Metastases are blood-borne and are most often found in bone, lungs and brain.
• Medullary carcinoma: This tumour arises from the parafollicular C cells of the thyroid. In addition to
calcitonin, the tumour may secrete 5-hydroxytryptamine (5-HT, serotonin), there is a genetic
predisposition that is inherited in an autosomal dominant fashion and is due to an activating mutation in
the RET gene .this forms part of one of the MEN syndromes
• Anaplastic carcinoma and lymphoma: The goitre is hard and there may be stridor due to tracheal
compression and hoarseness due to recurrent laryngeal nerve palsy. There is no effective treatment for
anaplastic carcinoma, although surgery and radiotherapy may be considered in some circumstances. In
older patients, median survival is only 7 months.

20. 7) Drug induced hyperthyroidism
• The anti-arrhythmic agent amiodarone has a structure that is analogous to that of T4 and contains
huge amounts of iodine. Amiodarone also has a cytotoxic effect on thyroid follicular cells and
inhibits conversion of T4 to T3 (increasing the ratio of T4:T3). Most patients receiving amiodarone
have normal thyroid function but up to 20% develop hypothyroidism or thyrotoxicosis, and so
thyroid function should be monitored regularly. TSH provides the best indicator of thyroid
function.

21. 8) Factitious hyperthyroidism
• thyrotoxicosis that occur following deliberate intake of thyroxine to reduce weight,usually in
emotionally disturbed person. Clues for diagnosis are high thyroid hormones and low radioiodine
uptake. Thyroglobulin level is zero or low. There is high ratio of T4:T3 = 70:1 (in conventional
thyrotoxicosis, the ratio is 30:1). Combination of negligible radioiodine uptake, high T4:T3 ratio
and low thyroglobulin is diagnostic.

22. Management of hyperthyroidism
• 1) beta blockers : non selective
• 2) Anti thyroid drugs
• Carbimazole
• Propythiouracil
• Usually, this renders the patient clinically and biochemically euthyroid at 6–8 weeks.
At this point, the dose can be reduced and titrated to maintain T4 and TSH within
their reference range.
• Adverse effects are rash and agranulocytosis.

23. • 3) radioactive iodine I 131
• Disadvantage of 131I treatment are: hypothyroidism,exacerbation of Grave’s
ophthalmopathy . In women of reproductive age, pregnancy must be excluded before
administration of 131I and avoided for 6 months thereafter.
• 4) surgery
• Indications of surgery:
• * Large goiter or multinodular goiter
• *Relapse or no response to drug
• * Drug hypersensitivity
• *Noncompliance with drug
• * Suspicion of malignancy
• * Pressure effect
• *Cosmetic purpose.

24. Complications of surgery:
*Hypothyroidism
* Transient hypoclcemia
*Permanent hypoparathyroidism (1%)
*Recurrent laryngeal nerve palsy, causing hoarseness of voice due to vocal cord palsy
• Complications of surgery:
• *Hypothyroidism
• * Transient hypoclcemia
• *Permanent hypoparathyroidism (1%)
• *Recurrent laryngeal nerve palsy, causing hoarseness of voice due to vocal cord palsy

25. • Complications of surgery:
• *Hypothyroidism
• * Transient hypoclcemia
• *Permanent hypoparathyroidism (1%)
• *Recurrent laryngeal nerve palsy, causing hoarseness of voice due to vocal cord palsy

26. Special conditions
• Pregnancy
• Thyroiditis
• Thyroid crisis

27. Hypothyroidism
• Clinical features :
• 1)Weight gain
• 2)Cold intolerance
• 3) Fatigue, somnolence
• 4)Dry skin,Dry hair, Alopecia, perorbital puffiness
• 5) Menorrhagia, Infertility, Galactorrhoea
• 6)Constipation
• 7) Hoarseness of voice
• 8)Depression
• 9) Loss of lateral eyebrows, Anaemia,Carotenaemia,Erythema ab igne
• 10) Bradycardia ,hypertension
• 11)Delayed relaxation of reflexes
• 12) ascites,Pericardial and pleural effusions

28. Causes
• 1)Hashimoto’s thyroiditis: the most common cause of hypothyroid goitre .it is autoimmune disease
result in lymphoid infiltration of the thyroid with positive thyroid peroxidase antibodies (anti TPO)
• 2)Spontaneous atrophic hypothyroidism
• 3) Iodine deficiency e.g. In mountainous regions
• 4)Iatrogenic :Radioactive iodine ablation ,Thyroidectomy ,Drugs:Antithyroid drugs ,Amiodarone,Lithium
• 5)Transient thyroiditis:Subacute (de Quervain’s) thyroiditis ,Post-partum thyroiditis
• 6) Congenital: Dyshormonogenesis (pendred syndrome is a combination of congenital hypothyroidism
and deafness) ,Thyroid aplasia .
• 7)Infiltrative:Amyloidosis, Riedel’s thyroiditis, sarcoidosis.
• 8)Secondary hypothyroidism: TSH deficiency
• 9) Graves’ disease with TSH receptor- blocking antibodies

30. Investigations
• Thyroid function tests: serum T4 is low and TSH is elevated in primary hypothyroidism while T4
and TSH are both low in secondary hypothyroidism.
• Anti thyroid peroxidase antibodies ( anti – TPO) is elevated in Hashimoto disease.
• ECG shows sinus bradycardia , low- voltage complexes and ST-segment and T-wave abnormalities.
• Non specific abnormalities:raised creatine kinase, aspartate aminotransferase, lactate
dehydrogenase (LDH), Hyponatraemia
• Hypercholesterolaemia
• Anaemia: normochromic normocytic or macrocytic

31. Management
• *levothyroxine replacement.start with a low dose of 50 μg/day for 3 weeks, increasing to 100
μg/day for a further 3 weeks and finally to a maintenance dose of 100–150 μg per day.
Levothyroxine has a half-life of 7 days so it should always be taken as a single daily dose and at
least 6 weeks should pass before repeating thyroid function tests (as TSH takes several weeks to
reach a steady state) and adjusting the dose.
• * Patients feel better within 2–3 weeks. Reduction in weight and periorbital puffiness occurs
quickly but the restoration of skin and hair texture and resolution of any effusions may take 3–6
months.The dose of levothyroxine should be adjusted to maintain serum TSH within the reference
range.

32. Special conditions
• 1) pregnancy
• 2) myxdema coma