Pre-clinical hypothyroidism
(Subclinical hypothyroid disease)
  Frank Barnhill M.D.

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Subclinical or preclinical hypothyroidism is often “inadvertently” found during screening for general diseases and more specifically when a person has very mild symptoms of depressed thyroid function.

Symptoms and signs of thyroid hormone deficiency (hypothyroidism) include:

  • Fatigue
  • Depressed mood
  • Poor concentration and thought processing
  • Dry skin
  • Unexplained weight gain
  • Low pulse rate
  • Hypersensitivity to cold temperatures
  • Constipation

In the general population, about 8 percent of women and 3.5 percent of men will suffer from preclinical hypothyroid disease. Unfortunately, in persons over age 60, those numbers can go as high as 15 percent for women and 8 percent for men!

Once found to have subclinical hypothyroidism, a person would have a 4 to 5 percent per year risk of developing full-blown hypothyroidism.

What could cause this condition to occur?

The most common cause in the United States is Hashimoto’s thyroiditis, a disease in which our body’s immune system mistakenly attacks the thyroid gland for some unknown reason. This condition can follow “other infections” by months or years. Inadequate treatment of full-blown hypothyroidism is another common reason for a person to experience subclinical hypothyroidism.

How is the diagnosis made?

The diagnosis of any type of preclinical disease relies on blood laboratory testing. The condition subclinical hypothyroidism exists when blood tests show normal levels of the thyroid hormone T4, but high levels of the thyroid stimulating hormone TSH. TSH levels are normally between 0.35 and 6.2 micro-units per milliliter of blood serum. A TSH level elevated above 6.2 normally indicates the thyroid gland is not producing sufficient or normal levels of Thyroxin or T4.


Key Note: There are several other conditions which may cause elevation of TSH levels in the face of normal T4 levels. These include:

  • Adrenal insufficiency
  • An acute serious illness, infection or severe injury
  • A TSH producing tumor
  • Medications such as metoclopramide
  • The normal variation in TSH production occurring between morning and night (This is called diurnal variation and occurs with a lot of hormones.)

In preclinical hypothyroidism, the TSH level goes up before there is clinical evidence of thyroid gland failure. Once again, this “window of opportunity” exists to give us the option of treating the condition in hopes of preventing the full blown disease and all of the bad things that can occur as a result of hypothyroidism.

So, why should we treat preclinical hypothyroidism?

Most specialists would agree the most common reason would be to prevent the condition from progressing to hypothyroidism and help avoid all of the side effects of the disease. Treating preclinical hypothyroidism should:

  • Improve a person’s mood, including anxiety, depression and irritability
  • Help a person’s ability to focus and concentrate
  • Lower LDL cholesterol (bad cholesterol)
  • Improve a person’s risk for heart and blood vessel diseases (this is still investigational)
  • Overall improve a person’s quality of life.

While there is not total agreement about how best to treat preclinical hypothyroidism among research physicians and those of us who practice clinical medicine, any person experiencing the above listed symptoms, should see his or her family doctor for evaluation. Most doctors will avoid starting thyroxin replacement until the TSH level rises to levels between 9 and 10.

What should you do if you have preclinical hypothyroidism and your doctor feels it’s too early to treat?

  • If you have symptoms of hypothyroidism appeal his decision or seek another opinion
  • If you have no symptoms or they are not bothersome, you should repeat your blood T4 and TSH levels minimum once yearly or when any symptoms erupt

Maybe this information will help you or someone you love avoid developing full blown hypothyroidism.

After all, our goal in detecting the preclinical diseases is to help you live a long, healthy, satisfying life without suffering the side effects of overt diseases like hypothyroidism hypertension and diabetes mellitus.

 Hopefully, one day we will be able to detect “pre clinical versions” of all diseases and we can all concentrate on improving our lives in creative ways.

Dr. Frank

These health tips are offered for your common sense use and are not intended to take the place of a visit to your doctor.  Your use of the materials implies your understanding that nothing herein contained represents individual medical advice.

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