Thyrotoxicosis Flashcards
What is thyrotoxicosis
The syndrome resulting from an excess of circulating free thyroxine (T4) and / or free triiodothyronine (T3)
What might cause thyrotoxicosis
Either increased thyroid hormone synthesis (hyperthyroidism) or
Increased release of stored thyroid hormone from an inflamed thyroid gland (subacute thyroiditis
What is primary hyperthyroidism characterised by
Raised free T4 and or T3 and low TSH
TSH is suppressed due to the negative feedback effect of thyroid hormones on TSH synthesis / secretion
What is secondary hyperthyroidism characterised by
Raised T4 and T3 due to increased TSH secretion from a pituitary tumour
Wyat is subclinical hyperthyroidism defined as
Suppressed TSH in the presence of normal free T4 and T3
What accounts for the majority of hyperthyroidism
Grave’s disease
What is the most common cause of hyperthyroidism in the elderly
Toxic multinodular goitre
What are some of the causes of thyrotoxicosis
Grave's disease Toxic multinodular goitre Toxic adenoma Thyroiditis Secondary hyperthyroidism Metastatic thyroid cancer
What causes Grave’s disease
Autoantibodies that stimulate the TSH receptor and hence thyroid hormone synthesis and secretion, and thyroid growth
What are some precipitating and predisposing factors of Grave’s disease
Genetic susceptibility (association with certain alleles of CTLA-4 and HLA) environmental factors such as infection
What are toxic multi nodular goitre and toxic adenoma the result of
Focal and / or diffuse hyperplasia of thyroid follicular cells whose function is independent of regulation by TSH
How can thyroiditis resit in thyrotoxicosis
By the release of preformed thyroid hormones from a damaged thyroid gland into the circulation
How can amiodarone affect thyroid function
Inhibits the conversion of T4 to T3
Results in a high or high-normal free T4
What are the clinical presentations of a patient with thyrotoxicosis
Heat intolerance, anxiety, irritability, hyperactivity, fatigue, insomnia
Increased sweating, warm moist skin, palmar erythema
Onycholysis, hair loss
Eyelid retraction or lag, proptosis, periorbital oedeama, increased tear production
Plaplitations
Widened pulse pressure
Exertional breathlessness
Diarrhoea, increased appetite, weight loss, dysphagia
Tremor, proximal muscle weakness, brisk tendon reflexes, inability to concentrate
Depression
Oligomennorhoea
Gynaecomastia, reduced libido, erectile dysfunction, polyuria
Osteoporosis
Goitre!
What is the pathogenesis of Graves’ ophthalmopathy
Involves activated T cell cytokines and TSH receptor antibodies that activate TSH receptors on fibroblasts and adipocytes. This sets of an inflammatory process and causes the secretion of hydrophilic glycosaminoglycans, resulting in an increased retro-orbital volume
What is a condition that is specific to Graves?
Pretirbial myxoedema
Results from an accumulation of hydrophilic glucosaminoglycans secreted by fibroblasts in the dermis
Describe the appearance of pretibila myxoedema
Raised, pigmented, orange-peel textured joules or plaques on the anterior aspect of the leg or the dorsum of the foot
Usually asymptomatic but may be pruritic or painful
What does thyroid acropachy resemble
Clubbing
Due to periosteal new bone formation in the phalanges
What is a thyroid storm also known as
Thyrotoxic crisis
How might a thyroid storm present
Fever, sweating
Cardiovascular symptoms: tachyarrhythmias, cardiac failure
Neuro: agitation, delirium, seizure, coma
GI : diarrhoea, vomiting, jaundice
What might cause a thyroid storm
Thyroid surgery, radio-iodine, iodinated contrast agents, withdraw of thionamides (antithyroid drugs) and acute illnesses including infection, stroke DKA or trauma
What are some investigations for thyroxicosis
Thyroid function tests:
What thyroid function test results diagnose primary hyperthyroidism
Suppressed serum TSH and high free T4 and or free T3
What thyroid function test results indicate secondary hyperthyroidism
TSH is either high or inappropriately normal in the presence of raised T4/T3
What thyroid function test results indicate subclinical hyperthyroidism
TSH is low, but free T4 and T3 levels are normal
What investigation is useful in differentiating between different causes of thyrotoxicosis
Radioisotope uptake scan
What is characterised by a diffuse increased uptake of the radioisotope
Grave’s disease
What would be seen if a toxic multi nodular goitre was present on radioisotope uptake scan
Multiple areas of increased radioisotope uptake with suppression of uptake in the rest of the gland
What would be seen if a solitary adenoma was present on radioisotope uptake scan
Single area of increased radioisotope uptake with suppression of uptake i the rest of the gland
What would be seen if thyroiditis was present on radioisotope uptake scan
A low or absent radioisotope
What must patients not take prior to a radioisotope uptake scan
Any iodine-containing medications, supplements or radio contrast dyes
MUST not be pregnant
What form of antibodies are positive in Grave’s disease
TSH receptor-stimulating antibodies
Test is expensive
What is elevated in patients with subacute viral de Quervain’s thyroiditis
Erythrocyte sedimentation rate (ESR)
What should be requested in cases of secondary hyperthyroidism
A pituitary MRI
What are the 3 options for treatment in thyrotoxicosis
Antithyroid drugs (thionamides)
Radio-iodine
Surgery (thyroidectomy)
What else could be give for patients with severe thyrotoxic symptoms
Beta blockers e.g. propranolol
What is the treatment for Grave’s disease in those below 50
Antithyroid drugs as initial treatment
if thyrotoxicosis relapses, surgery or radio-iodine is preferred
What is the treatment for Graves’ disease in those over 50
Radio-iodine or surgery
What is the primary treatment for men with Graves’ disease
Radio-iodine due to the high relapse rate in men
How are patients with toxic multi nodular goitre and toxic adenoma treated
Ideally with radio-iodine or surgery depending on patient’s preference
Anti-thyroid drugs may be used in those who refuse or are unsuitable for surgery
What are some antithyroid drugs
carbimazole
methimazole
propylthiouracil (PUT)
How do antithyroid drugs work
They reduce T4 and T3 production by inhibiting thyroid peroxidase
What is an advantage of taking carbimazole over other drugs
Only has to be taken once daily
Describe the dosage of antithyroid drugs in Graves’ disease
Titration regimen
Start of high and gradually reduce over 4-8 weeks to maintenance dose
What is a rare but significant complication of antithyroid drugs
Agranulocytosis
What are the symptoms of agranulocytosis
Fever
sore throat
mouth ulcers
any sign of infection
What is some advice for patients with suspected agranulocytosis
Stop treatment immediately
Full blood count checked ASAP
What might happen if a patient with agranulocytosis has a neutrophil count of less than 0.5x10^9/L and a sore throat
May required admission and treatment with granulocyte colony-stimulating factor and antibiotics
What are a common side effect of antithyroid drugs. What should be done for this
Rashes and pruritus
Treat with antihistamines without stopping treatment
What are some other side effects of antithyroid drugs
Macular rash Nausea vomiting abnormal taste/ smell arthralgia pruritus lymphadenopathy deranged LFTs
PTU may rarely be associated with what
Anti-neutrophil cytoplasmic antibody positive vasculitis
How often should a patient on an antithyroid drug regimen be followed up
6 weekly for 6 months
6 monthly for 2 years
Annually
How is radio-iodine administered
Orally as a capsule or solution
How long do antithyroid drugs need to be discontinued for prior to radio-iodine commencing
about 3 days
This allows uptake of the isotope by the thyroid gland
What happens to the dose in patients with renal failure
It must be significantly reduced
Why is radio=iodine contraindicated in pregnancy and breast feeding
It destroys fetal thyroid
How long must a patient who has received radio-iodine treatment wait before conceiving
4 months
Radio-iodine is associated with an exacerbation of what
Graves’ ophthalmopathy
Why is surgery not an ideal treatment for Graves’
It is associated with a higher rate of hypothyroidism or recurrent hyperthyroidism depending on how much of the thyroid is removed
What are some of the risks associated with thyroid surgery
Hypoparathyroidism
recurrent laryngeal nerve damage
laryngeal oedema (due to bleeding int the neck )
In what cases is surgery chosen over radio-iodine
Patients with large goitres causing upper airway obstruction or dysphagia
Patients who cannot take antithyroid drugs and are either pregnant or have moderate/ severe Graves’ ophthalmopathy
What is the treatment for mild ophthalmopathy symptoms
Artificial tears during the day and ointments
eye shades
elevation of the head and neck
avoid sleeping on the face
What is the treatment for severe ophthalmopathy symptoms
IV methylprednisolone
decompression surgery
radiotherapy
How is subacute and postpartum thyroiditis treated
NSAIDs if mild
Steroids and NSAIDs for moderate or severe
How is thyroid hormone resistance characterised by
Reduced responsiveness of the tissues to thyroid hormone
What symptoms of thyroid hormone resistance may patients present with
Goitre Tachycardia ADHD , learning disability Growth retardation Recurrent ENT infection
