THYROID DISEASE Flashcards
What is the axis of thyroid hormone production?
Hypothalamus produces TRH.
Anetrior pituitary produces TSH.
The thyroid hormone produces T4 and T3.
Thyroid hormones are lipophilic and so cannot dissolve in blood. What two proteins are involved in the transport of thyroid hormones? And what percentage of thyroid hormone is carried by each?
Thyroid binding globulin- 70%
Albumin- 30%
How are t3 and t4 formed?
Biosynthesis of thyroid hormones requires iodine as a substrate. Iodine is actively transported via sodium/iodide symporters into follicular thyrocytes where it is organified onto tyrosyl residues in thyroglobulin first to produce monoiodotyrosine (MIT) and then diiodotyrosine (DIT). Thyroid peroxidase (TPO) then links to DITs to form the two ringed structure t4, and MIT to DIT to form t3and reverse t3.
What percentage of circulating t3 is secreted from the thyroid gland?
20%
What is the first line test in diagnosing primary hyper/hypothyroidism?
Serum TSH
What is the major antibody found in Grave’s disease?
Anti-TSHR
What is the major antibody found in autoimmune hypothyroidism?
Anti-TPO
What is thyroid scintiscanning? What is it used for?
Permits localisation of sites of accumulation of radioiodine which gives information about the iodine trap.
to define areas of high and low function
To distinguish between Grave’s and thyroiditis
To detect retrosternal goitre
To detect ectopic thyroid tissue
What is the most accurate test for the diagnosis of thyroid nodules?
Fine needle aspiration cytology
What are the 5 causes of hyperthyroidism in order of prevalence?
Grave’s disease
Toxic nodular goitre
Thyroiditis: can be drug induced, post-partum, autoimmune, post-viral
Exogenous iodine = usually iatrogenic (overtreatment of hypothyroidism, Amiodarone, _Radiocontrast iodine dye_s) or Factitious (common in healthcare professionals)
TSH secreting Pituitary Adenoma
What are the common cardiovascular, neurological and gastrointestinal symptoms of hyperthyroidism?
Cardiovascular = Tachycardia, SOB, ankle swelling, degeneration to AF
Neurological = tremor, myopathy, anxiety
GI = ¯weight loss, diarrhoea, appetite
Which cause of hyperthyroidism leads to eye and skin involvement? What are the eye and skin signs of this hyperthyroidism cause?
Effects on the eyes and skin are more characteristic in Grave’s disease (IgG TSHr Ab) rather than other causes of hyperthyroidism:
Eyes = lid lag, periorbital puffiness, proptosis, and ophthalmoplegia leading to diplopia.
Skin = develop pretibial myxoedema, vitiligo, thyroid acropachy
What is NOSPECs? What is the TEARS mnemonic for management of thyroid eye disease?
A grading scale of thyroid eye disease
N—No signs or symptoms O—Only signs (such as lid retraction), no symptoms S—Soft tissue involvement P—Proptosis E—Extraocular muscle involvement C—Corneal involvement S—Sight loss.
T—Tobacco abstinence is immensely important E—Euthyroidism must be achieved and maintained A—Artificial tears are helpful for the majority of patients and can afford rapid relief from the symptoms of corneal exposure R—Referral to a specialist centre with experience and expertise in treating thyroid eye disease is indicated in all but the mildest of cases S—Self-help groups can provide valuable additional support
What is the first line management of hyperthyroidism?
- Prescribe propranolol 20-80mg TD for immediate symptom management
- Thionamides are co-prescribed:
- Carbimazole is prescribed at >20mg OD, the pt is then followed up at 6 weekly intervals. Once remission occurs the pt is titrated down to 5mg for 18 months. For 40% of patients this will be sufficient.
- Propylthiouracil can also be tried but has the added risk of hepatotoxicity.
What is the block and replace regimen?
- In the Block and replace regimen the patient is given 40mg Carbimazole until Euthryoid and is then prescribed an additional 100µg Levothyroxine for 6m. This has worse S/E, but is faster
What is the second line therapy for hyperthyroidism?
-
Radio-iodine (iodine-131) = a dose of 500-800MBq depending on the cause of hyperthyroidism, after 7 days following withdrawal of thionamides. It should be given with steroids where patients have ophthalmopathy
- Relative contraindication where patients has ongoing thyroid eye disease
- CI in pregnancy and breastfeeding, or where the patient cannot avoid close contact with children for a few weeks
- Risks = Hypothyroidism, slightly risk of cancer / infertility
What is the third line therapy for hyperthyroidism?
Surgery
What is the most serious SE of carbimazole?
Agranulocytosis- therefore warn patients about sore throat
What is the triad of imaging used to determine the aetiologies of a goitre?
- USS can show thyroid nodules and differentiate solid vs. cystic nodules. It can also show signs suggestive of malignancy e.g. irregularity or calcification
- Iodine-123 uptake scanning can show if there is a ‘hot’ nodule, or if the whole thyroid is overactive
- FNAC is used on all goitres and nodules to see if they are benign (thy2, needs x2 samples 6 months apart to confirm) or suspicious/malignant (thy3/4/5). If the FNAC is insufficient (thy1) it is repeated using US guidance
List at least 5 differentials for a Goitre?
Hashimoto thyroiditis
Graves disease
Familial or sporadic multinodular goitre
Iodine deficiency
Follicular adenoma
Colloid nodule or cyst
Thyroid cancer
What is subclinical hyperthyroidism?
Subclinical hyperthyroidism is a condition in which you have low levels of thyroid stimulating hormone (TSH) but normal levels of T3 and T4.
Give 4 categories of causes of hypothyroidism.
- Atrophic thyroiditis following autoimmune disease (Hashimoto’s), post-viral (DeQuervains), Post-partum
- Iatrogenic = following treatment for Hyperthyroidism or drug induced e.g. Lithium
- Iodine deficiency = uncommon in the UK
- Congenital due to Thyroid agenesis or Enzyme defects
What are the signs and symptoms of hypothyroidism?
- Cardiovascular = Bradycardia, HF, Pericardial effusion
- Neurological = depression, psychosis, carpal tunnel syndrome
- GI = weight, constipation
- Skin = myxoedema, Erythema ab igne, vitiligo
What is the management of hypothyroidism?
Levothyroxine 100ug OD
