The thyroid gland Flashcards
Hyperthyroidism
Is where there is over-production of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4), by the thyroid gland
Thyrotoxicosis
refers to the effects of an abnormal and excessive quantity of thyroid hormones in the body
Primary Hyperthyroidism
Is due to thyroid pathology. The thyroid is behaving abnormally and producing excessive thyroid hormone.
Secondary Hyperthyroidism
is due to pathology in the hypothalamus or pituitary. The pituitary gland produces too much thyroid-stimulating hormone, stimulating the thyroid gland to produce excessive thyroid hormones.
Subclinical hyperthyroidism
is where the thyroid hormones (T3 and T4) are normal and thyroid-stimulating hormone (TSH) is suppressed (low). There may be absent or mild symptoms.
Graves Disease
is an autoimmune condition where TSH receptor antibodies cause primary hyperthyroidism. These TSH receptor antibodies, produced by the immune system, stimulate TSH receptors on the thyroid. This is the most common cause of hyperthyroidism.
Toxic multinodular goitre
(also known as Plummer’s disease) is a condition where nodules develop on the thyroid gland, which are unregulated by the thyroid axis and continuously produce excessive thyroid hormones. It is most common in patients over 50 years.
Causes of hyperthyroidism
GIST
Graves’ disease
Inflammation (thyroiditis)
Solitary toxic thyroid nodule
Toxic multinodular goitre
Causes of thyroiditis
De Quervain’s thyroiditis
Hashimoto’s thyroiditis
Postpartum thyroiditis
Drug-induced thyroiditis
Hyperthyroidism presentation
Anxiety and irritability
Sweating and heat intolerance
Tachycardia
Weight loss
Fatigue
Insomnia
Frequent loose stools
Sexual dysfunction
Brisk reflexes on examination
Graves disease specific features
Diffuse goitre (without nodules)
Graves’ eye disease, including exophthalmos
Pretibial myxoedema
Thyroid acropachy (hand swelling and finger clubbing)
Solitary toxic thyroid nodule
A solitary toxic thyroid nodule is where a single abnormal thyroid nodule acts alone to release excessive thyroid hormone. The nodules are usually benign adenomas. Treatment involves surgical removal of the nodule
Management of hyperthyroidism
Carbimazole is the first-line anti-thyroid drug, usually taken for 12 to 18 months. Once the patient has normal thyroid hormone levels (usually within 4-8 weeks), they continue on maintenance carbimazole and either:
The carbimazole dose is titrated to maintain normal levels (known as titration-block)
A higher dose blocks all production, and levothyroxine is added and titrated to effect (known as block and replace)
Propylthiouracil is the second-line anti-thyroid drug. It is used in a similar way to carbimazole. There is a small risk of severe liver reactions, including death, which is why carbimazole is preferred.
MHRA alert carbimazole
The MHRA issued a warning in 2019 about the risk of acute pancreatitis in patients taking carbimazole. In your exams, look out for a patient on carbimazole presenting with symptoms of pancreatitis (e.g., severe epigastric pain radiating to the back).
carbimazole and propylthiouracil cautions
Both carbimazole and propylthiouracil can cause agranulocytosis, with a dangerously low white blood cell counts. Agranulocytosis makes patients vulnerable to severe infections. A sore throat is a key presenting feature of agranulocytosis. In your exams, if you see a patient with a sore throat on carbimazole or propylthiouracil, the cause is likely agranulocytosis. They need an urgent full blood count and aggressive treatment of any infections.
Iodine treatment rules
Women must not be pregnant or breastfeeding and must not get pregnant within 6 months of treatment
Men must not father children within 4 months of treatment
Limit contact with people after the dose, particularly children and pregnant women
Hypothyroidism
refers to insufficient thyroid hormones, triiodothyronine (T3) and thyroxine (T4).
Primary hypothyroidism
is where the thyroid behaves abnormally and produces inadequate thyroid hormones. Negative feedback is absent, resulting in increased production of TSH. TSH is raised, and T3 and T4 are low
Secondary hypothyroidism
also called central hypothyroidism, is where the pituitary behaves abnormally and produces inadequate TSH, resulting in under-stimulation of the thyroid gland and insufficient thyroid hormones. TSH, T3 and T4 will all be low.
causes of primary hypothyroidism
Hashimoto’s thyroiditis is the most common cause of hypothyroidism in the developed world. It is an autoimmune condition causing inflammation of the thyroid gland. It is associated with anti-thyroid peroxidase (anti-TPO) antibodies and anti-thyroglobulin (anti-Tg) antibodies.
Iodine deficiency is the most common cause of hypothyroidism in the developing world. In the UK, iodine is particularly found in dairy products and may be added to non-dairy milk alternatives (e.g., soya milk).
Treatments for hyperthyroidism have the potential to cause hypothyroidism:
Carbimazole
Propylthiouracil
Radioactive iodine
Thyroid surgery
What drugs can cause hypothyroidism
Lithium inhibits the production of thyroid hormones in the thyroid gland and can cause a goitre and hypothyroidism.
Amiodarone interferes with thyroid hormone production and metabolism, usually causing hypothyroidism but can also cause thyrotoxicosis.
causes of secondary hypothyroidism
Secondary hypothyroidism is often associated with a lack of other pituitary hormones, such as ACTH, referred to as hypopituitarism. This is rarer than primary hypothyroidism, and may be caused by:
Tumours (e.g., pituitary adenomas)
Surgery to the pituitary
Radiotherapy
Sheehan’s syndrome (where major post-partum haemorrhage causes avascular necrosis of the pituitary gland)
Trauma
presentation of hypothyroidism
Weight gain
Fatigue
Dry skin
Coarse hair and hair loss
Fluid retention (including oedema, pleural effusions and ascites)
Heavy or irregular periods
Constipation
