Thyroids

Question 1

Thyroid gland introduction

Answer 1

Largest pure endocrine gland
Located in the anterior neck
2 lobes connected by an isthmus
Controls metabolism via thyroid hormones

Question 2

Anatomy of the thyroid

Question 3

Physiology of thyroid gland

Answer 3

Made up of 2 types of cells
Closely packed follicular- iodine containing thyroid hormones T3 and T4-majority of the tissue
Parafollicular cells- Calcitonin

Follicular cells take up iodide an amino acids from circulation on the basolateral side -synthesise thyroglobulin and thioperoxidase from A. acids
These are then secreted into thyroid follicles together with iodide
Follicular cells then take up iodinated thyroglobulin from follicles by endocytosis, extract thyroid hormones into blood.
Thyroid hormones are transported throughout the body where they control metabolism
Normally 80% T4 and 20% T3 is produced

Question 4

Categories and effect of thyroid glands

Question 5

Diseases of the thyroid

Answer 5

Congenital
Inflammation
Functional abnormality
Goitres
neoplasia

Question 6

Goitres

Answer 6

Thyroid disease may present as a swelling, a disordered metabolism or a combination-7% of the world’s population has a goitre, mostly as a result of iodine deficiency.

Question 7

Thyroid swellings can be classified as follows:

Answer 7

• Diffuse goitre
• Multinodular goitre
• Solitary thyroid nodule
Patients may present with any combination of a normal or large thyroid coupled with hypo-, eu or hyperthyroidism

Question 8

Treatment

Answer 8

Medical:thyroxine analogues –levothyroxine
Conservative-cosmesis concerns
Surgical –thyroidectomy

Question 9

Indications for surgery of a multinodular goitre

Answer 9

Local symptoms, eg significant or symptomatic retrosternal extension, dysphagia, tracheal deviation or
Stenosis
• Enlarging dominant nodule, unless unequivocally benign
• RLN palsy
• Cosmesis
• Hyperthyroidism

Question 10

Thyroid cancers

Answer 10

70% papillary carcinoma: affects young people; 95%+ survival
• 20% follicular carcinoma: not able to diagnose on FNAC; 95%+ survival
• 5%medullary carcinoma: C-cell multifocal cancer. May be part of MEN syndrome; genetic testing is required
• <5%anaplastic carcinoma: terrible prognosis. Seen in older patients
• Lymphoma: needs chemotherapy under the care of the haemato-oncologists. Good prognosis
Treatment:surgery,radiotherapy

Question 11

Inflammatory thyroiditis

Answer 11

Acute thyroiditis: bacterial cause (usually streptococci)
• Subacute thyroiditis (de Quervain’s thyroiditis): viral cause (Epstein–Barr virus [EBV], mumps, measles)
• Chronic thyroiditis (Hashimoto’s thyroiditis): autoimmune cause

Question 12

Hypothyroidism (myxoedema)

Answer 12

Iatrogenic causes (90% cases) include:
• Post-iodine-131 therapy
• Post-thyroidectomy
• Post-radiotherapy
• Drugs:
Carbimazole and propylthiouracil: used as treatment of hyperthyroidism to block thyroid
peroxidase enzyme
• Amiodarone: used as treatment for atrial fibrillation; contains iodine and can cause
hyperthyroidism and hypothyroidism. Thyroid function tests (TFTs) should be checked every 6 months
• Lithium: used as mood stabiliser in bipolar affective disorder
Idiopathic myxoedema
Autoimmune diseases: eg Hashimotos thyroiditis
Iodine deficiency
Hypopituitarism
Tumour infiltration

Question 13

Treatment of hypothyroidism

Answer 13

Oral T4 for life.
T4 has a predictable biological activity and is cheap. It has a long half-life (1 week).TFTs can be checked to ensure that the patient is euthyroid.

Question 14

Emergency

Answer 14

Myxoedema coma Elderly patients with undiagnosed hypothyroidism, or those who have not taken their medication,can present with:
altered mental status
coma
bradycardia
hypothermia
hypoglycaemia.
TFTs should always be checked in patients with this clinical picture. Patients should be resuscitated on ITU with fluids, gentle rewarming, and T3 and T4 supplementation. Ventilation may be necessary.

Question 15

Hyperthyroidism

Answer 15

Three causes account for 99% of cases:
• Graves’ disease (autoimmune) accounts for 90% of cases
• Toxic adenoma
• Toxic multinodular goitre (Plummer’s disease)

Question 16

Other causes of hyperthyroidism

Answer 16

Drugs such as thyroxine (the Jod–Basedow effect is induction of thyrotoxicosis in a previously
euthyroid individual by the over-treatment of multinodular goitre with iodine)
Carcinoma (rare)
Iodine-131 treatment
Hyperfunctioning ovarian teratoma
(struma ovarii)
Subacute/acute thyroiditis
TSH-secreting tumour (eg hydatidiform mole, choriocarcinoma, pituitary tumour)

Question 17

Graves disease

Answer 17

Graves’ disease is an immunological disorder of unknown aetiology characterised by stimulation of TSH receptors by immunoglobulins or antibodies.
It is classically seen in women aged 20–40 years.
Pathophysiology of Graves’ disease
Thyroid-stimulating immunoglobulins or thyroid-receptor antibodies attach to TSH receptors on the surface of the thyroid follicular cell and cause excess secretion of T3 and T4

Question 18

Clinical features of Graves disease

Answer 18

• Hyperthyroidism
• 85% have eye signs
• Diffuse goitre
• Thyroid acropachy (similar to clubbing)
• Pretibial myxoedema
• Thyroid bruit on auscultation due to increased vascularity

Question 19

Eye disease in hyperthyroidism

Answer 19

Three-quarters of patients with Graves’ disease have associated eye signs.
1.Exophthalmos is due to:
Proptosis: caused by increased retrobulbar orbital fat and enlarged intraorbital muscles
infiltrated with lymphocytes and containing increased water and mucopolysaccharide
2. Lid retraction: due to a direct effect of thyroxine on the orbital muscles
3. Orbital oedema
Erythema of the conjunctiva is seen in association with the lid retraction. In severe cases,
paralysis of the ocular muscles can lead to squint, diplopia and, rarely, optic nerve damage.

Question 20

Treatment of Graves’ disease

Answer 20

medical
carbimazole
Propylthiouracil and carbimazole are thionamides that inhibit thyroid peroxidase and hence block the organification and coupling process in the thyroid follicular cell, and thus reduce thyroid hormone synthesis
radioiodine
surgical