20 - Thyroid and Adrenal Endocrinology Flashcards
What is the difference between primary and secondary gland failure?
Primary: end organ hormone low but pituitary hormone high
Secondary: end organ hormone high and pituitary hormone low
What structures lie close to the thyroid gland?
- Parathyroid glands posteriorly
- Superior and inferior thyroid arteries
- Recurrent laryngeal nerve
What is a thyroglossal cyst and how can you tell it is a thyroid lump on examination?
Thyroid starts in the base of the tongue and travels down. Some remnant tissue can be left behind on the travels forming a cyst
Lump will move up with swallowing and sticking tongue out
What cells are present in the thyroid and what is their role?
Follicular cells: Synthesise thyroglobulin which is then iodinated to form thyroxine which is stored in the colloid
C-Cells/Neuroendocrine cells: Secrete calcitonin
What malignancy causes high calcitonin levels?
Medullary thyroid cancer
Thyroid hormone is made from iodinated tyrosine. What do they bind to travel in the blood?
Carried by the following to nuclear receptors:
- TBG
- Albumin
- Transthyretin
How do you do a thyroid examination?
1. General Inspection: agitated, fidgety
2. Hands: peripheral tremor paper, pulse rate and rhythm
3. Face: inspect eyebrows/skin/sweating, exopthalmous, eye movements, lid lag
4. Thyroid: inspect, swallow water, protrude tongue, palpate
5. Lymph nodes
6. Trachea: deviation in goitre
7. Percuss: retrosternal dullness
8. Auscultate: bruits in Grave’s
9. Special Tests: biceps, pretibial myxedema, proximal myopathy
What is included in a TFT panel, and what can affect this panel?
- TSH
- Free T3 and T4
Amount of TBG. More TBG can increase total T3/T4 but doesn’t mean free T3/T4 has increased!!!
Pregnancy, Illness, Lithium and Amiodarone can derange TFTs so do TFTs on relatively well person
What thyroid tests should you look at for hyperthyroidism and what will they show?
T3, T4, TSH
Primary Hyperthyroidism (issue with thyroid): Low TSH, Raised T3 and Raised T4
Secondary Hyperthyroidism (thyroid being stimulated): Raised TSH, Raised T3 and Raised T4. This is rare and often due to TSH secreting pituitary adenoma
What thyroid tests should you look at for hypothyroidism and what will they show?
TSH and only T4
Primary Hypothyroidism (autoimmune): raised TSH, low T4
Secondary Hypothyroidism (pituitary issue): low TSH, low T4
Apart from a standard TFT panel, what other investigations can you do for thyroid pathology?
- Thyroid autoantibodies e.g TPO, anti-TSH, anti-TG
- Serum thyroglobulin
- US
- Scintigraphy
What are some signs and symptoms of hyperthyroidism (a.k.a thyrotoxicosis)?
Due to increased sympathetic action
Symptoms: weight loss, insomnia, irritability, anxiety, heat intolerance, palpitations, tremor, diarrhoea, sweating, oligomenorrhea, infertility
Signs: sinus tachycardia, AF, fine tremor, palmar erythema, thin hair, lid lag due to increased sympathetic tone, hyperreflexia, goitre, bruits
How may hyperthyroidism present differently in the elderly and children?
Elderly: paradoxically with reduced energy levels, known as apathetic thyrotoxicosis
Children: typical symptoms plus accelerated growth and behavioural disturbance
What are some of the signs of hyperthyroidism due to Grave’s disease?
Due to cross reactivity with TSH receptors in back of orbit and skin
- Eyes: lid retraction, exophthalmos, opthalmoplegia
- Pretibial myxoedema: above lateral malleoli
- Thyroid acropachy: clubbing, painful toe and finger swelling
- Goitre
What are some of the different causes of hyperthyroidism?
Grave’s (most common): autoimmune, usually women 40-60, IgG antibodies that can stimulate TSH receptors in thyroid, orbit and skin. Associated with other autoimmune conditions and can be triggered by stress, infection, pregnancy
Nodular Hyperthyroidism: can be toxic adenoma or toxic multinodular goitre that releases T3/T4. More in elderly than Grave’s
Ectopic Thyroid tissue: metastatic follicular thyroid cancer, struma ovarii
Thyroiditis: inflammation of thyroid due to viral infection, child birth or medication like amiodarone
What autoantibody is present in Grave’s disease?
TSH receptor autoantibody (stimulates TSH)
What investigations should you do to diagnose hyperthyroidism and find the underlying cause? What do these tests show?
TFTs: low TSH, raised free T3/T4
Thyroid autoantibodies: TPO, TSHrAB
Bloods: normocytic anaemia, raised Ca, raised LFTs, raised ESR, neutropenia in Grave’s
US: for nodular disease
Isotope Scan (Te/Iodine): Grave’s will have uniform uptake, nodular disease will only have increased uptake in nodular areas, thyroiditis will not have uptake
What is subclinical hyperthyroidism and how is it managed?
Low TSH
Normal T3/T4
Only treat if symptoms
What are the different treatment options for hyperthyroidism?
Medical (1st Line)
- Thionamides: carbimazole and propylthiouracil
- Beta-blockers: propanolol to control symptoms rapidly
Surgical:
- Thyroidectomy
Radioactive Iodine:
- Single dose of I-131
How do you start someone on Carbimazole for hyperthyroidism?
Two methods:
Titration: Take 20-40mg/day for 4 weeks then titrate according to TFTs
Block-Replace: Give carbimazole-levothyroxine simultaneously to prevent iatrogenic hypothyroidism.
If Grave’s keep on for 12-18 months then withdraw. If relapse need surgery or radioactive iodine
What do you need to warn people about when starting them on carbimazole? (Thionamide)
- Will take 4-6 weeks to normalise thyroid levels
- Risk of agranulocytosis (bone marrow suppression) (If unexplained fever/sore throat need urgent FBC to exclude pancytopenia. Stop drug if neutrophils low)
- May get generalised rash but will stop when stop taking drug
The definitive treatment of hyperthyroidism is radioactive iodine or surgery, driven by patient choice. What are the disadvantages of radioactive iodine?
I131
- Contraindications: pregnancy and lactation
- Can flare up eye disease
- Common post-treatment hypothyroidism that needs lifetime levothyroxine
- Patient emits small amount of radiation after so needs to avoid pregnant people and children for a few weeks
What are the complications of thyroidectomy surgery used to treat hyperthyroidism?
- Hoarse voice if damage recurrent laryngeal nerve
- Bleeding
- Infection
- Hypoparathyroidism so low Ca
Control thyroid before surgery and use beta-blockade during anaesthetic induction to prevent peri-op AF
What are some of the complications of hyperthyroidism that is left untreated or poorly treated?
- Heart failure
- Angina
- AF
- Osteoporosis
- Opthalmopathy
- Gynaecomastia
- Thyroid storm
What are some signs and symptoms of thyroid eye disease?
Symptoms: eye discomfort, incresed tear production, photophovia, diplopia
Signs: exophthalmos, proptosis, papilloedema, opthalmoplegia
How is thyroid eye disease managed?
- Control hyper/hypothyroidism
- Stop smoking (biggest risk factor)
- Artificial tears
- High dose steroids if severe
- Surgical decompression if severe
What are some causes of a goitre?
What are some signs and symptoms of hypothyroidism?
Symptoms (similar to depression): weight gain, constipation, fatigue, cold intolerance, menorraghia, poor memory
Signs: bradycardia, hyporeflexia, dry skin, non-pitting oedem, round puffy face, thickening of skin
Often subtle signs/symptoms and diagnosed incidentally
What are some of the causes of hypothyroidism?
Primary (high TSH)
- Hashimotos: commoner in women
- Iodine deficiency!!!!!!!!
- Drug induced: anti-thyroid drugs, amiodarone, lithium, iodine
- Post thyroidectomy/Iodine treatment/Radiation Therapy
- Pregnancy induced
Secondary: (low TSH)
- Hypopituitarism: low fT4 and low TSH, investigate pituitary
What autoantibodies are present in Hashimoto’s disease?
TPO: thyroid peroxidase antibodies
TG: antithyroglobulin
What are some causes of hypothyroidism in neonates/infancy?
Iodine deficiency: causes severe mental retardation (cretinism)
Familial thyroid dyshormonogenesis: autosomal recessive defect in thyroid hormone synthesis
What are some investigations done to diagnose hypothyroidism and what do they show?
TFTs: high TSH (low in secondary), low fT4
TPO: diagnoses autoimmune hypothyrodism
Triglycerides/Cholesterol: raised
How is hypothyroidism treated?
LEVOTHYROXINE
- Starting dose usually 50-100ug, if elderly or IHD then 25ug
- Check TSH at 4 weeks on blood test
- Want TSH to be normal not suppressed
- If secondary then get T4 to upper normal because cannot rely on TSH
- Once right levels check TSH yearly
When someone is being treated with levothyroxine, what are the causes of a persistently high TSH or suppressed TSH?
- Persistently high (underreplacement)
- Poor compliance
- Malabsorption (Crohn’s, PPI)
- Suppressed (overreplaceement)
What are the risks of over replacement with levothyroxine?
- AF
- Osteoporosis
Why can amiodarone cause thyroid issues?
Iodine rich drug that is structurally like T4
- Hypothyrodism: iodine excess
- Hyperthyroidism: destructive thyroiditis causing hormone release
Check TFTs 6 monthly on Amiodarone
What is subclinical hypothyroidism and how is it managed?
- Elevated TSH but normal T3/T4
- If asymptomatic do not treat as often spontaneously resolves
- If TSH>10 and asymptomatic start treatment as high risk of progression
- If planning pregnancy or symptomatic start treatment
- If positive thyroid antibodies check TFTs yearly
What are some signs and symptoms of a thyrotoxic crisis?
Lifethreatening hypermetabolic state by excess release of thyroid hormone
- Agitation
- Confusion
- Coma
- Tachycardia
- Hypertension
- AF
- Acue abdomen
- Heart failure
What are some triggers of a thyrotoxic crisis?
- Untreated hyperthyroidism
- Recent thyroid surgery or radioiodine
- Infection
- MI
- Trauma