21.2 Thyroid disease

Question 1

What is the thyroid gland?

Answer 1

An endocrine organ in the anterior midline of the neck, sat in front of the trachea and just below the thyroid cartilage.
2 lobes connected by an isthmus.

Question 2

What cell types are found in the thyroid and what are their functions?

Answer 2

• Thyroid follicular cells: produce triiodothyronine (T3) and thyroxine (T4) which control the metabolic rate
• Parafollicular cells: secrete calcitonin which reduce calcium levels

Question 3

Describe the development of the thyroid.

Answer 3

• Downgrowth of formane caecum (at the junction between the anterior two thirds and posterior third of tongue)
• Descends through the tongue, past the hyoid and to its midline position in the neck
• If a portion of the tract remains patent, a thyroglossal cyst can form

Question 4

How is a thyroglossal cyst diagnosed?

Answer 4

It will appear as a midline swelling which moves on tongue protrusion and swallowing.
Confirmed via ultrasound or other imaging.

Question 5

What is the difference between triiodothyronine and thyroxine?

Answer 5

• T3 is the active form
• T4 is the inactive form, converted to T3 in peripheral tissues

Levothyroxine is a manufactured form of T4 used to treat hypothyroidism.

Question 6

What are the functions of T3 and T4?

Answer 6

Regulates metabolic rate: affects carbohydrate, protein and lipid metabolism
- Thyroxine also potentiates the actions of other hormones such as catecholamines and growth hormones

Question 7

Describe the hypothalamic-pituitary-thyroid feedback system.

Answer 7

• Hypothalamus releases thyrotropin releasing hormone (TRH) to the anterior pituitary
• Anterior pituitary released thyroid stimulating hormone (TSH) to the thyroid gland
• Thyroid gland is stimulated to produce T3 or T4

Question 8

What do you call a thyroid swelling that is visible?

Answer 8

A goitre

Question 9

What % of thyroid swellings are benign?

Answer 9

95%

Question 10

What does it mean when a thyroid nodule is described as “hot” or toxic”?

Answer 10

Means the thyroid is producing excess/additional thyroid hormones.

Question 11

What symptoms may be associated with a thyroid lump?

Answer 11

• Dysphagia
• Odynophagia (pain on swelling)
• Stridor
• Hoarseness
• Can cause shortness of breath if pressing on trachea

Question 12

Does a goitre always mean changes in thyroid hormones?

Answer 12

No, a goitre can occur with or without hormone changes.

Question 13

What features are unique regarding the goitre present in Grave’s disease?

Answer 13

In Grave’s, the goitre has it’s own blood supply.
If a stethoscope is used you may hear excess blood supply- audible whooshing noise.

Question 14

What is a diffuse thyroid enlargement indicative of?

Answer 14

• Grave’s
• Endemic goitre
• Hashimoto’s thyroiditis

Question 15

What is a single thyroid node indicative of?

Answer 15

• Cyst
• Benign tumour (adeoma)
• Malignancy

Question 16

What is a multinodular goitre indicative of?

Answer 16

• Iodine deficiency

Question 17

What are the differential diagnoses for thyroid lumps?

Answer 17

Diagnoses for a lump in the neck which moves during swallowing:
- Thyroglossal cyst
- Multinodular goitre
- Hashimoto’s thyroiditis
- Graves’ disease
- Thyroid adenoma
- Thyroid carcinoma
- Laryngocele

Question 18

What investigations are carried out for thyroid lumps?

Answer 18

• Bloods: thyroid function tests (TFTs) which measure levels of T3, T4 and thyroid antibodies
• Imaging: ultrasound
• Cytology/biopsy: fine needle aspiration alongisde ultrasound

Question 19

What are the 3 thyroid antibodies?

Answer 19

• Thyroid peroxidase antibody: the antibody present in Hashimoto’s thyroiditis and Graves’ (fewer)
• Thyroglobulin antibody: autoimmune thyroid disease
• TSH receptor antibody: an antibody against the TSH receptor leading to high levels of thyroid hormones

Question 20

Describe hypothyroidism.

Answer 20

• Very common
• 10 times more common in women
• Low T3 and T4
• Everything slows down

Question 21

What investigation is carried out for hypothyroidism?

Answer 21

• Thyroid function test: TSH is variable, T3 and T4 are low

Question 22

What is the treatment for hypothyroidism?

Answer 22

Life long oral thyroxine replacement e.g. Levothyroxine

Question 23

What are the causes of hypothyroidism?

Answer 23

• Inadequate dietary iodine (endemic goitre)
• Primary hypothyroidism: disease of the thyroid itself. Autoimmune thyroid desturction (Hashimoto’s- thyroid peroxidase antibody destroys the thyroid), drugs (lithium, amiodarone, radioactive iodine), thyroid tumour.
• Secondary hypothyroidism: disease of the pituitary gland or brain which is affecting TRH or TSH.

Question 24

Explain Hashimoto’s thyroiditis.

Answer 24

• Most common cause of hypothyroidism in the UK
• Autoimmune disorder, anti-thyroid peroxidase antibodies destroy the thyroid
• Most commonly seen in women over 50
• Antibodies directly attack thyroid cells causing swelling and gradual reduction in T3 and T4

Question 25

What is the name for hypothyroidism in children?

Answer 25

Congenital hypothyroidism or cretinism

Question 26

Describe the clinical presentation of hypothyroidism in children and adults.

Answer 26

! Myxoedema = deposition of mucin substances resulting in thickening of the skin and subcutaneous tissues, sign of severe disease, multiple organs affected, can lead to coma or death (often comes up in exams) !!!!

Question 27

What is the dental relevance of hypothyroidism in children?

Answer 27

• HypOdontia
• Delayed dental development
• Thick lips, enlarged tongue
• PeriO risk
• Caries risk

Question 28

What is the dental relevance of hypothyroidism in adults?

Answer 28

• MacroglOssia
• PeriO risk
• Altered taste
• Delayed wound healing

Question 29

What should you remember when treating patients with hypothyroidism?

Answer 29

• May have lower pain thresholds
• Sensitivity/unpredictable response to CNS depressants: sedatives, opioids, GA
• Avoid treating patients with severe untreated thyroid disease- RISK OF MYXODEMATOUS COMA due to stress of dental tx

Question 30

Describe hyperthyroidism.

Answer 30

• Excessive thyroxine production
• Common
• 5 times more common in women
• Often caused by anti-TSH receptor antibodies attacking the thyroid gland
• Also caused by toxic multinodular goitre and toxic nodule

Question 31

How is hyperthyroidism diagnosed?

Answer 31

• Through thyroid function tests
• Thyroid antibody tests
• Ultrasound if there is suspected enlargement/nodule of the gland

Question 32

Describe Grave’s disease.

Answer 32

• Caused by anti-TSH receptor antibodies resulting in low TSH and high T3 and T4
• Toxic, diffuse goitre
• Grave’s opthalmopathy: bulging and lid retraction, pressure and puffiness, can lead to sensitivity to light and vision loss
• Shins have an orange peel appearance and thickened skin with dimples

Question 33

What are the symptoms of hyperthyroidism?

Answer 33

• Abnormal heart rate: too fast or irregular (AF)
• Increased appetite and weight loss
• Sweaty skin
• Hand tremors
• Heat intolerance

Question 34

How is hyperthyroidism treated?

Answer 34

• Beta blockers: treat symptoms of overexcitement of the body e.g. high HR
• Carbimazole, radioactive iodine destruction or thyroidectomy
• The latter tx require levothyroxine afterwards to compensate for lack of function

Question 35

What is the dental relevance of hyperthyroidism?

Answer 35

• Don’t treat pts with untreated or severe hyperthyroidism
• May be sensitive to adrenaline as their heart rate is already elevated or irregular