Wk 1 - Symposium 1: Clinical Aspects of Thyroid Function Flashcards
What are the functions of the thyroid hormones?
- Regulates basal metabolic rate
- Increases the gain/responsiveness to catecholamines “permissive action or cooperative”
- Affect protein synthesis, help regulate long bone growth (synergy with growth hormone)
- Important for development, growth and neural differentiation
- T4 is a prohormone (ie inactive – further activated in peripheral tissue)
What nerve supplies the thyroid?
Recurrent laryngeal nerve (sometimes injured during surgery)
If the parathyroid glands are injured during surgery, a patient would suffer from…
Hypocalcaemia
What are the different diseases that can affect the thyroid (divided into function or structural)?
- Functional
- Overactivity, hyperthyroidism “thyrotoxicosis”
- Under activity, hypothyroidism
- Structural
- Growth, Goitre
- Nodules
- Combined (often patients come in with both)
List the causes of hyperthyroidism (primary, iatrogenic, secondary, gestational, genetics).
-
Primary
- Graves’ disease- most common aetiology
- Toxic adenoma or toxic multinodular goitre
- Thyroiditis
- Iatrogenic:
- Jod-Basedow (iodine-induced)
- Exogenous thyroid hormone
- Drug-induced e.g. amiodarone/ lithium
-
Secondary
- Rare (TSH producing pituitary tumours) - TSHoma
- Gestational (hCG-induced-)
- Genetics- thyroid hormone resistance ( rare)
_____ is the most common primary cause of hyperthyroidism.
Graves’ disease is the most common primary cause of hyperthyroidism.
List the clinical features of thyrotoxicosis
Symptoms:
- Weight loss
- Increased appetite
- Palpitations
- Diarrhoea
- Heat intolerance
- Anxiety, irritability
- Fine tremor
- Fatigue
- Eyes- dry/reduced vision
- Menstrual irregularities
Signs - sympathetic overdrive:
- Tachycardia
- Atrial fibrillation
- Proximal weakness
- Diaphoresis/ Moist skin
- Fine hair
- Systolic hypertension
- Tremor
- Thyroid stare / proptosis
- Goitre- smooth / nodular
How does thyrotoxicosis (hyperthyroidism) look on investigations (TSH, T3 and T4)?
-
Primary:
- Low/suppressed TSH
- Increased fT3 and/or fT4 (T3 rises before T4)
-
Secondary:
- TSH elevated or not suppressed
- Increased fT3 and/or fT4
- Thyroid antibodies – TPO/TSH receptor antibodies (positive in Graves’ disease)
- Imaging – Isotope scan/Ultrasound
What is Graves’ disease?
- Autoimmune disorder- familial
- Thyroid stimulating immunoglobulin binds TSH receptor (TSH receptor antibodies- TRAb)
List the classic triad of Graves’ disease.
- Hyperthyroidism (90%)
-
Ophthalmopathy (20-40%)
- proptosis, ophthalmoplegia, conjunctival irritation
- 3-5% of cases require directed treatment
-
Dermopathy (0.5-4.3%) – less common these days
- localized myxedema, usually pretibial (skin becomes like orange peel)
- especially common with severe ophthalmopathy
List some other autoimmune diseases often associated with the presence of Graves’ disease.
- Vitiligo
- Pernicious anaemia (B12 deficiency)
- Addison’s disease
- Premature ovarian failure
- Type 1 diabetes
- Coeliac disease
The second most common cause of hyperthyroidism is…
Toxic adenoma- single and multiple
What is toxic adenoma?
- Thyroid adenomas are benign lesions of the thyroid gland.
- These lesions may be inactive or active, producing thyroid hormones. In this case, they may be referred to as toxic thyroid adenomas.
- Patients with thyroid adenomas are usually asymptomatic.
- However, biochemical and clinical hyperthyroidism can be caused by a toxic adenoma, which is defined as an autonomously functioning thyroid nodule (AFTN).
What is thyroiditis?
- The term thyroiditis reflects inflammation of the thyroid gland.
- Destruction of thyroid cells causes the release of hormones.
List the possible causes of thyroiditis.
- Autoimmune eg Hashimoto, Graves
- Infectious
- Drug-related eg amiodarone, lithium
- Can occur post-partum
Describe the mechanism of action of anti-thyroid medications.
Act on different stages of thyroid hormone synthesis see picture
