Internal Diseases and Therapy · MU Sofia

79. Thyrotoxicosis. Hyperthyroidism.

Covers thyrotoxicosis as a syndrome of excess thyroid hormone, with a classification of its causes into hyperthyroid and nonhyperthyroid forms, including Graves disease, toxic nodular disease and thyroiditis. It then describes classic and general symptoms and signs, the TSH and T4 interpretation for overt and subclinical disease, and a labelled thyroid scintigram comparison. Management is outlined by drug choice, pregnancy considerations, radioiodine and surgery, followed by thyroid storm and the distinction between hyperthyroidism and thyrotoxicosis.

Inside: 1 section · 2 labelled pictures · 13 flashcards · 3 min

Topic 80 of 139 in the MU Sofia syllabus for Internal Diseases and Therapy (Medicine, Years 4 and 5). The free AceMed note covers it in 1 section, about 499 words (3 min of reading), with 13 flashcards.

In this note

  1. Thyrotoxicosis. Hyperthyroidism

Thyrotoxicosis. Hyperthyroidism

Thyrotoxicosis

This is a systemic syndrome caused by exposure to excessive thyroid hormone. It has a range of different etiologies that are listed and categorised below:

  • Hyperthyroidism
  • Antibody-mediated stimulation of thyroid tissue
  • Graves disease
  • Autonomously functioning thyroid tissue
  • Toxic multinodular goiter
  • Toxic adenoma
  • Iodine exposure
  • Excessive TSH secretion
  • TSH secreting pituitary adenoma
  • Nonhyperthyroid thyrotoxicosis
  • Ingestion of exogenous thyroid hormone
  • Inflammation causing release of endogenous thyroid hormone (subacute/autoimmune thyroiditis)

Of these causes, Graves is the most common cause, accounting for 60% of cases of hyperthyroidism. In Graves the gland is stimulated by autoantibodies that bind to and activate the TSH receptor. This TSH-receptor stimulation (not TSH, which is suppressed) causes hyperthyroid secretion.

The classic symptoms of thyrotoxicosis include weight loss (despite appetite), heat intolerance, palpitations, tremor and hyperdefecation. Other general symptoms include fatigue, insomnia, anxiety, irritability and weakness. Signs include tachycardia, systolic hypertension with widened pulse pressure, moist skin, onycholysis and staring gaze with lid lag (exophthalmos in graves).

In graves we also see goiter, while in toxic multinodular goiter, as the name suggests nodules should be palpable. Pretibial myxoedema may also be visible, as might thin, brittle hair.

In patients with suspected thyrotoxicosis, diagnosis can be confirmed by measurement of TSH and T4. Overt thyrotoxicosis is characterised by suppressed TSH and elevated T4 and T3, while subclinical thyrotoxicosis is where there is suppressed TSH with T4 and T3 in the

normal range. Take a look at the image below to better understand how to interpret these results.

Investigations of patients with suspected thyrotoxicosis should be:

  • Obtain TFTs (likely show raised T3 and T4 but lower TSH)
  • Autoantibody testing to look for graves or other causes (look for Anti-TSH Ab)
  • Radio-iodine uptake scans can help demonstrate diffuse uptake in graves, or nodular uptake in toxic multinodular hyperthyroidism
  • Other investigations as needed

Thyroid scans: A normal; B Graves disease (diffuse increased uptake); C toxic multinodular goitre (patchy uptake); D toxic adenoma (single hot nodule); E thyroiditis (almost no uptake).

Image: “Thyroid scintigraphy” by Petros Perros, CC BY-SA 3.0, via Wikimedia Commons.

Management

  • Antithyroid treatment such as carbimazole and methimazole are most widely used
  • Beta blockers may also be needed in the short term to reduce BMP
  • Avoid carbimazole and methimazole in the first trimester of pregnancy, use propylthiouracil instead
  • Radioactive iodine may be used as treatment in refractory cases
  • Thyroidectomy as third line

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