Hypothyroidism

Question 0

What is subclinical hypothyroidism? What is the upper limit of normal for a TSH value?

Answer 0

Subclinical hypothyroidism is present when TSH is elevated but free thyroxine is normal.

Presently there is considerable controversy as to the appropriate upper limit of normal for serum TSH. Most laboratories have used values of about 4.5 to 5.0 mU/L. A monograph published by the National Academy of Clinical Biochemistry argues that the upper limit of normal of the euthyroid reference range should be reduced to 2.5 mU/L because 95 percent of rigorously screened euthyroid volunteers have serum values between 0.4 and 2.5 mU/L [6]. However, a population study from Germany, which excluded patients with a positive family history, goiter, nodules, or positive anti-TPO antibodies, found a normal reference range of 0.3 to 3.63 mU/L [7]. The use of 2.5 mU/L as the upper limit of normal for serum TSH will increase substantially the number of patients in the United States diagnosed with subclinical hypothyroidism. Presently, controversy exists as to whether patients with serum TSH values between 5 and 10 mU/L require treatment (see “Subclinical hypothyroidism”). Until there are data demonstrating an adverse biologic significance for serum TSH values between 2.5 and 5.0 mU/L, the wisdom of labeling such patients as hypothyroid is questionabl

Question 1

What is the most common cause of hypothyroidism?

Answer 1

Chronic autoimmune (Hashimoto's) thyroiditis
The most common cause of hypothyroidism in iodine-sufficient areas of the world is chronic autoimmune (Hashimoto's) thyroiditis, which is caused by cell- and antibody-mediated destruction of thyroid tissue [1]. The disorder has two forms: goitrous and atrophic. They differ in the extent of lymphocytic infiltration, fibrosis, and thyroid follicular cell hyperplasia of the thyroid gland, but not in their pathophysiology.

Question 2

Some important facts about treating subclinical hypothyroidism:

Answer 2

There is controversy regards treatment of TSH in the range of 5 to 10. Most would treat the value over 10.5. There is little evidence that treating A TSH between five and 10 is necessary if the free thyroxine is normal.

• A slight TSH elevation will often be normal on repeat testing.
• Many patients with subclinical hypothyroidism will never become clinically hypothyroid.
• Some physicians will use the level of TPO(thyroid peroxide antigen) -antibody elevation as a measure of likelihood of progressing to clinical hypothyroidism. ** A patient with a negative assay for these TPO antibodies is much less likely to progress to overt hypothyroidism.

-in the absence of significant symptoms it’s unlikely treatment of subclinical hypothyroidism will be of benefit.

Question 3

What are the two forms of autoimmune Hashimoto’s thyroiditis?

Answer 3

goitrous autoimmune thyroiditis and atrophic autoimmune thyroiditis

Question 4

What is the potential downside of treating subclinical hypothyroidism?

Answer 4

Many patients taking thyroid hormone become sub clinically hyperthyroid manifest as a suppressed TSH. There is some evidence that subclinical hyperthyroidism can lead to bone loss, atrial fibrillation, left ventricular hypertrophy, congestive heart failure and coronary artery disease.

Several studies of octogenarians revealed that those with subclinical hypothyroidism actually fared better than those with a normal TSH level!