21.2 Thyroid disease Flashcards
(35 cards)
What is the thyroid gland?
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.
What cell types are found in the thyroid and what are their functions?
- Thyroid follicular cells: produce triiodothyronine (T3) and thyroxine (T4) which control the metabolic rate
- Parafollicular cells: secrete calcitonin which reduce calcium levels
Describe the development of the thyroid.
- 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
How is a thyroglossal cyst diagnosed?
It will appear as a midline swelling which moves on tongue protrusion and swallowing.
Confirmed via ultrasound or other imaging.
What is the difference between triiodothyronine and thyroxine?
- 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.
What are the functions of T3 and T4?
Regulates metabolic rate: affects carbohydrate, protein and lipid metabolism
- Thyroxine also potentiates the actions of other hormones such as catecholamines and growth hormones
Describe the hypothalamic-pituitary-thyroid feedback system.
- 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
What do you call a thyroid swelling that is visible?
A goitre
What % of thyroid swellings are benign?
95%
What does it mean when a thyroid nodule is described as “hot” or toxic”?
Means the thyroid is producing excess/additional thyroid hormones.
What symptoms may be associated with a thyroid lump?
- Dysphagia
- Odynophagia (pain on swelling)
- Stridor
- Hoarseness
- Can cause shortness of breath if pressing on trachea
Does a goitre always mean changes in thyroid hormones?
No, a goitre can occur with or without hormone changes.
What features are unique regarding the goitre present in Grave’s disease?
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.
What is a diffuse thyroid enlargement indicative of?
- Grave’s
- Endemic goitre
- Hashimoto’s thyroiditis
What is a single thyroid node indicative of?
- Cyst
- Benign tumour (adeoma)
- Malignancy
What is a multinodular goitre indicative of?
- Iodine deficiency
What are the differential diagnoses for thyroid lumps?
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
What investigations are carried out for thyroid lumps?
- Bloods: thyroid function tests (TFTs) which measure levels of T3, T4 and thyroid antibodies
- Imaging: ultrasound
- Cytology/biopsy: fine needle aspiration alongisde ultrasound
What are the 3 thyroid antibodies?
- 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
Describe hypothyroidism.
- Very common
- 10 times more common in women
- Low T3 and T4
- Everything slows down
What investigation is carried out for hypothyroidism?
- Thyroid function test: TSH is variable, T3 and T4 are low
What is the treatment for hypothyroidism?
Life long oral thyroxine replacement e.g. Levothyroxine
What are the causes of hypothyroidism?
- 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.
Explain Hashimoto’s thyroiditis.
- 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
