The thyroid gland (located just below the front of our neck) makes thyroid hormone, called thyroxine, to help control many of our body functions. A thyroid disease can either produce too little thyroxine (Hypothyroid) or too much (Hyperthyroid); these two diseases, plus Thyroiditis, are described below.
The brain makes hormones which control the thyroid gland. To understand that relationship, & what the common lab tests wind up measuring (the tests can seem confusing), see Thyroid Physiology for a brief explanation.
Almost always due to an autoimmune disease called Hashimoto’s Thyroiditis, which we don’t know why it occurs (likely genetic). Its main symptom is fatigue. It can also cause weight gain, feeling cold, thickening of skin, voice change (hoarse), heavy menstrual periods, constipation, depression, memory loss, and more. Rarely might it lead eventually to coma. Treatment is easy — take thyroid hormone, usually produced as “Levo-thyroxine” (brand name is Synthroid®).
We diagnose Hypothyroidism by blood tests, finding an elevated TSH (thyroid stimulating hormone); once we see that’s high, we order a Free T4 (T4 = thyroxine) (see Thyroid Physiology for explanation of how the labs work). If the Free T4 is low, we’ve made the diagnosis & start treatment.
Sometimes the TSH is high but the Free T4 is normal. Then it depends: if TSH is >15 we treat; if TSH is <10 we often don’t treat; if TSH is 10-15 we muddle over it. A high TSH with normal Free T4 is called “subclinical hypothyroidism,” which may or may never become true Hypothyroidism. Suppose a patient has fatigue, we order a TSH and find subclinical hypothyroidism. It probably has nothing to do with the patient’s symptoms.
Hypothyroidism is most dangerous in early pregnancy, causing an 80% rate of miscarriage. Any woman with hypothyroidism needs to increase her medication dose around 30% if she becomes pregnant, and seek prenatal care right away. A newly-pregnant woman with subclinical hypothyroidism needs immediate thyroid tests, & should likely start treatment.
I’ve seen a number of patients diagnosed incorrectly, and wind up on treatment forever when they don’t need it. See “Thyroiditis” below.
Also an autoimmune disease, called Graves’ Disease, but not always (see below). Too much thyroid hormone (thyroxine) can cause fatigue, weight loss, rapid heartbeat (palpitations), tremors, nervousness, feeling hot, very light menstrual periods, hair loss, sleep problems, bone loss (osteoporosis). It may cause bulging eyes (exophthalmos) that can damage the cornea. It’s most dangerous to the heart, causing an irregular rhythm atrial fibrillation that may provoke a stroke. Graves’ Disease might also eventually cause heart failure.
We diagnose Graves’ by finding no TSH (thyroid-stimulating hormone) on a blood test (none at all, not just a low value). Once we find this, we order blood tests for Free T4 (T4 = thyroxine) and T3 (another thyroid hormone; see Thyroid Physiology for explanation of how the labs work). If the Free T4 and/or the T3 are high, and especially if we find signs of Graves’ on physical exam (bulging eyes, or maybe just “lid lag,” or a large smooth thyroid gland that’s not tender), we order additional lab tests: TSH-receptor antibody (“Trab”) and maybe a Thyroid Stimulating Immunoglobulin (TSI). The “Trab” is almost always positive in Graves’, but sometimes false-positive. The TSI proves Graves’ if positive, but may be false-negative. If in doubt, a radioactive iodine scan tells for sure.
It’s really important to prove the diagnosis for sure, because treatment involves suppressing or even destroying the thyroid gland. This can be done by medication like Methimazole (Tapazole®) or Propylthiouracil (PTU), by radiation, or by surgery. The patient usually then becomes Hypothyroid for life, & needs to take treatment for it (see above). This would be bad if they never had Graves’ disease to begin with; see “Thyroiditis” below.
With Graves’ Disease, we sometimes give medication to slow the heart rate if it’s very fast, and maybe anticoagulants (“blood thinners”) to prevent stroke if a patient has atrial fibrillation. Once the Hyperthyroidism is controlled, & these complications disappear, we can stop treatment for them.
Inflammation of the thyroid gland, which gets better on its own. There are 3 types:
- Painful Thyroiditis, caused by a virus
- Painless Thyroiditis, cause unknown
- Post-Partum Thyroiditis, painless, occurring up to a year after pregnancy
Each type of Thyroiditis begins with a hyperthyroid phase (but no eye abnormalities of Graves’ Disease). Then a hypothyroid phase follows with high TSH, low Free T4 (see “Hypothyroid” above). Finally, all thyroid tests become normal. During each phase, there may be symptoms.
Unfortunately, some patients coincidentally identified during the hypothyroid phase get diagnosed as “Hypothyroid” and put on medication forever. We may suspect this is if a patient winds up controlled on a low dose of Levo-thyroxine, like 25 micrograms (= 0.025 milligrams). Most patients with permanent Hypothyroidism need at least 100 mcg (= 0.1 mg), often much more. Anybody on merely 25 mcg should simply stop the medication and get retested in 2 months; if repeat thyroid tests stay normal they don’t need anything. Even worse, patients coincidentally identified during the hyperthyroid phase may get misdiagnosed as Graves’. Then they get their thyroid gland suppressed or even permanently destroyed. Never get told you have Graves’ Disease without a good explanation as to how the diagnosis was made.