Hyperthyroidism



Definitions

Hyperthyroidism is where there is over-production of thyroid hormone by the thyroid gland. Thyrotoxicosis refers to an abnormal and excessive quantity of thyroid hormone in the body.

Primary hyperthyroidism is due to thyroid pathology. It is the thyroid itself that is behaving abnormally and producing excessive thyroid hormone.

Secondary hyperthyroidism is the condition where the thyroid is producing excessive thyroid hormone as a result of overstimulation by thyroid stimulating hormone. The pathology is in the hypothalamus or pituitary.

Grave’s disease is an autoimmune condition where TSH receptor antibodies cause a primary hyperthyroidism. These TSH receptor antibodies are abnormal antibodies produced by the immune system that mimic TSH and stimulate the 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 that act independently of the normal feedback system and continuously produce excessive thyroid hormone.

Exophthalmos is the term used to describe bulging of eyeball out of the socket caused by Graves Disease. This is due to inflammation, swelling and hypertrophy of the tissue behind the eyeball that forces the eyeball forward.

Pretibial myxoedema is a dermatological condition where there are deposits of mucin under the skin on the anterior aspect of the leg (the pre-tibial area). This gives a discoloured, waxy, oedematous appearance to the skin over this area. It is specific to Grave’s disease and is a reaction to the TSH receptor antibodies.

Causes of Hyperthyroidism

  • Grave’s disease
  • Toxic multinodular goitre
  • Solitary toxic thyroid nodule
  • Thyroiditis (e.g. De Quervain’s, Hashimoto’s, postpartum and drug-induced thyroiditis)

 

Universal Features of Hyperthyroidism

  • Anxiety and irritability
  • Sweating and heat intolerance
  • Tachycardia
  • Weight loss
  • Fatigue
  • Frequent loose stools
  • Sexual dysfunction

 

Unique Features of Grave’s Disease

These features all relate to the presence of TSH receptor antibodies.

  • Diffuse goitre (without nodules)
  • Graves eye disease
  • Bilateral exophthalmos
  • Pretibial myxoedema

 

Unique Features of Toxic Multinodular Goitre

  • Goitre with firm nodules
  • Most patients are aged over 50
  • Second most common cause of thyrotoxicosis (after Grave’s)

 

Solitary Toxic Thyroid Nodule

This is where a single abnormal thyroid nodule is acting alone to release thyroid hormone. The nodules are usually benign adenomas. They are treated with surgical removal of the nodule.

De Quervain’s Thyroiditis

De Quervain’s Thyroiditis describes the presentation of a viral infection with fever, neck pain and tenderness, dysphagia and features of hyperthyroidism. There is a hyperthyroid phase followed by a hypothyroid phase as the TSH level falls due to negative feedback. It is a self-limiting condition and supportive treatment with NSAIDs for pain and inflammation and beta-blockers for symptomatic relief of hyperthyroidism is usually all that is necessary.

Thyroid Storm

Thyroid storm is a rare presentation of hyperthyroidism. It is also known as “thyrotoxic crisis”. It is a more severe presentation of hyperthyroidism with pyrexia, tachycardia and delirium. It requires admission for monitoring and is treated the same way as any other presentation of thyrotoxicosis, although they may need supportive care with fluid resuscitation, anti-arrhythmic medication and beta-blockers.

 

Hyperthyroidism Management

Information here is summarised from NICE CKS 2016. Treatment is guided by a specialist.

 

Carbimazole

Carbimazole is the first line anti-thyroid drug. It is usually successful in treating patients with Grave’s Disease, leaving them with normal thyroid function after 4-8 weeks. Once the patient has normal thyroid hormone levels, they continue on maintenance carbimazole and either:

  • The dose is carefully titrated to maintain normal levels (known as “titration-block”)
  • The dose is sufficient to block all production and the patient takes levothyroxine titrated to effect (known as “block and replace”)

Complete remission and the ability to stop taking carbimazole is usually achieved within 18 months of treatment.

 

Propylthiouracil

Propylthiouracil is the second line anti-thyroid drug. It is used in a similar way to carbimazole. There is a small risk of severe hepatic reactions, including death, which is why carbimazole is preferred.

 

Radioactive Iodine

Treatment with radioactive iodine involves drinking a single dose of radioactive iodine. This is taken up by the thyroid gland and the emitted radiation destroys a proportion of the thyroid cells. This reduction in functioning cells results in a decrease of thyroid hormone production and thus remission from the hyperthyroidism. Remission can take 6 months and patients can be left hypothyroid afterwards and require levothyroxine replacement.

There are strict rules where the patient:

  • Must not be pregnant and are not allowed to get pregnant within 6 months
  • Must avoid close contact with children and pregnant women for 3 weeks (depending on the dose)
  • Limit contact with anyone for several days after receiving the dose

Beta-blockers

Beta blockers are used to block the adrenalin related symptoms of hyperthyroidism. Propranolol is a good choice because it non-selectively blocks adrenergic activity as opposed to more “selective” beta blockers the work only on the heart. They do not actually treat the underlying problem but control the symptoms whilst the definitive treatment takes time to work. They are particularly useful in patients with thyroid storm.

 

Surgery

A definitive option is to surgically remove the whole thyroid or toxic nodules. This effectively stops the production of thyroid hormone, however the patient will be left hypothyroid post thyroidectomy and require levothyroxine replacement for life.

 

Last updated November 2018
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