USMLE Internal Medicine Review 10 04 Causes of Hypothyroidism in the US

USMLE Internal Medicine Review 10 04 Causes of Hypothyroidism in the US

On these “Gold Standard Internal Medicine Facts” pages you will find Free:

  • USMLE Audio Review files from our “Gold Standard USMLE Reviews”
  • Transcriptions of those files
  • And videos (as they become available)

The idea is that you can review for the USMLE online by:

  • Listening to the Audio
  • Following along with the transcription
  • Or by watching the video (if available)

If you like what you here, you can purchase the entire Gold Standard Foundations of Medicine MP3 Audio USMLE review for your iPhone, iPod, or computer here.

Let’s start our USMLE Review with Hypothyroidism and Hyperthyroidism from the Gold Standard USMLE Foundations of Medicine Audio Review program.

 

Play USMLE Audio MP3 10 04 Causes of Hypothyroidism in the US Below

 

Begin 10 04 Causes of Hypothyroidism in the US Transcription

We’ll look at the five most common causes of primary hypothyroidism in the US in order of frequency of occurrence. First, by far the most common cause of hypothyroidism in the US is what thyroid condition caused by diffuse lymphocytic infiltration of the thyroid gland resulting in diffuse goiter, progressive destruction of the parenchyma.

And hypothyroidism?

  • Hashimoto’s thyroiditis, also called Hashimoto’s disease.

Student doctor please pause the tape and repeat our description of Hashimoto’s thyroiditis.

  • Hashimoto’s thyroiditis or Hashimoto’s disease, the most common cause of hypothyroidism in the US, is a thyroid condition caused by diffuse, lymphocytic infiltration of the thyroid gland resulting in diffuse goiter, progressive destruction of the parenchyma, and hypothyroidism.

And what is the second most common cause of hypothyroidism?

  • (It is a mode of therapy for Grave’s disease) Radioactive Iodine therapy for Grave’s disease.

Third is, which surgical therapy for Grave’s disease or for nodular goiter?

  • Subtotal thyroidectomy.

Fourth is, excessive intake of what substance from things like kelp tablets, radio-contrast dyes or the anti-arrhythmic drug, Amiodarone?

  • Excessive intake of Iodide.

Fifth is, what variant of thyroiditis?

  • Subacute thyroiditis.

Rarer causes of hypothyroidism in the US include iodide deficiency, other goitrogens like antiemetic agents lithium, or antithyroid drugs, Propylthiouracil and Methimazole.

And which type of in-born error?

  • In-born error of thyroid hormone synthesis.

Student doctor please stop the tape and repeat the five most common causes of primary hypothyroidism in the US in order of frequency of occurrence, along with three rarer causes.

  • The most common cause by far of hypothyroidism in the US is Hashimoto’s thyroiditis, also called Hashimoto’s disease, followed by radioactive iodine therapy for Graves’ disease, subtotal thyroidectomy, excessive intake of iodide, and subacute thyroiditis.  Rarer causes include iodide deficiency, other goitrogenic agents like lithium, Propylthiouracil  and Methimazole, and in-born error of thyroid hormone synthesis.

Looking now at three variants of Hashimoto’s thyroiditis. The first is Hashimoto’s associated with goiter usually in younger patients.

The second is neonatal hypothyroidism due to placental transmission of what type of antibodies?

  • Transmission of TSH release blocking antibodies.

And the third variant of Hashimoto’s thyroiditis is idiopathic thyroid atrophy, presumably end-stage autoimmune thyroid disease.

This often follows which disease synonymous with ophthalmic hyperthyroidism and pares disease?

  • Graves’ disease.

Student doctor please pause the tape and summarize the three variants we’ve mentioned of Hashimoto’s thyroiditis.

  • Variants of Hashimoto’s thyroiditis include Hashimoto’s associated with goiter  more common in younger patients, neonatal hypothyroidism due to placental transmission of TSH release blocking antibodies and idiopathic thyroid atrophy, presumably end-stage autoimmune thyroid disease following Graves disease.

We mentioned that Hashimoto’s thyroiditis is more likely to be associated with goiter in younger patients.

In older patients, the thyroid gland may be totally destroyed by the immunologic process with the only trace of disease being a persistently positive test for which auto-antibodies? 

  • In older patients, often the only trace of Hashimoto’s disease will be a persistently positive test for TPO which are thyroid microsomal  auto-antibodies.

Moving on now to the pathogenesis of hypothyroidism. Thyroid hormone deficiency affects every tissue in the body, so hypothyroid symptoms are bound to be many. There are two factors accounting for the interstitial edema characteristic of hypothyroidism and particularly evident in the skin, heart muscle and striated muscles.

First is accumulation of what hydrophilic substance in interstitial tissues?

  • (Starts with a G) Accumulation of glycosaminoglycans in interstitial tissues.

What is the predominant asset in glycosaminoglycans?

  • Hyaluronic acid.

And the second factor causing interstitial edema in hypothyroidism is increased capillary permeability to which type of simple protein?

  • (starting with A) Increased capillary permeability to albumin.

Is the accumulation of glycosaminoglycans due to the excessive synthesis of or decreased destruction of glucosaminoglycans?

  • Decreased destruction.

Student doctor please pause the tape and summarize our initial comments on the pathogenesis of hypothyroidism. Please include the reason why hypothyroid symptoms are many and two factors accounting for the interstitial edema characteristic of hypothyroidism.

  • Thyroid hormone deficiency affects every tissue in the body, so hypothyroid symptoms are bound to be many. There are two factors accounting for the interstitial edema characteristic of hypothyroidism, particularly evident in the skin, heart muscle and striated muscle. These are accumulation of glycosaminoglycans in interstitial tissues and increase capillary permeability to albumin. The accumulation is due to decreased destruction rather than excessive synthesis of glycosaminoglycans.

****END OF TRANSCRIPTION****

 

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