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If you are hypothyroid, the first question you probably have is, “What caused my underactive thyroid?” In the U.S., your doctor will often test your thyroid peroxidase (TPO) antibodies to help determine if you have Hashimoto’s thyroiditis, an autoimmune disease that’s a common cause of hypothyroidism in Americans. Elevated antibodies indicate that your immune system is attacking your thyroid gland. Over time, when you have Hashimoto’s disease, your thyroid may not produce enough thyroid hormone.
An estimated 30 million+ Americans are hypothyroid, but the exact percentage of people with an underactive thyroid gland due to Hashimoto’s thyroiditis is unknown. It is known, however, that Hashimoto’s is the most common cause of hypothyroidism in the U.S.
What if you’ve been diagnosed with hypothyroidism, but antibody tests show no evidence of Hashimoto’s? What caused your hypothyroidism? Ahead, a look at how you can be hypothyroid without testing positive for Hashimoto’s disease.
First, even if you don’t show elevated thyroid antibodies, you can still have Hashimoto’s thyroiditis. Research has found that about 10% of patients with Hashimoto’s are antibody negative. Additionally, about 5% of patients diagnosed with Hashimoto’s thyroiditis based on clinical grounds – or confirmed by ultrasound or biopsy – have no measurable thyroid antibodies.
Some healthcare practitioners recommend that, in the absence of any other clear cause, patients should still follow guidelines for managing autoimmune Hashimoto’s. Incorporating an anti-inflammatory diet, lifestyle changes, and focusing on improving immune health can’t hurt – and may help if you have “stealth” Hashimoto’s disease.
Iodine is a mineral that’s needed to manufacture and synthesize thyroid hormones. If you don’t have enough iodine in your diet, your thyroid gland can’t make enough thyroid hormone, leaving you hypothyroid. Iodized salt has eliminated widespread iodine deficiency in the U.S. Still, people who follow a low-salt or salt-free diet can sometimes have a deficiency in this essential mineral.
Before you start supplementing with iodine or dramatically increasing your iodine intake from food, it’s a good idea to test your iodine levels. There are three ways to test your iodine levels:
- A urine test is quick and easy but may not be as accurate as other tests. You can get results in minutes, and it measures the amount of iodine in your urine
- A blood test is simple and accurate, but it takes a few days to get results.
- The iodine loading test is the most accurate way to measure iodine levels. You take a dose of iodine in supplement form, then collect your urine over a 24-hour. The amount of iodine you excrete is then measured. The test is more time-consuming and takes time to get your results.
A note: You may hear people recommend that you test for iodine deficiency by painting liquid iodine on your skin and seeing how fast it is “absorbed.” This test is not an accurate way to evaluate your iodine levels.
Some babies are born with a defective or absent thyroid gland or a genetic defect that affects the synthesis or function of thyroid hormones. Hypothyroidism from birth is known as congenital hypothyroidism. Most newborns are tested for congenital hypothyroidism right after birth, during the routine heel-stick test.
While in most cases, the symptoms of congenital hypothyroidism become evident early, it is possible to have congenital hypothyroidism and not know it if newborn screening tests are not performed. This situation is rare, however.
If part or all of your thyroid gland is removed surgically, for example, to treat thyroid cancer or goiter, this can result in hypothyroidism. Radioactive iodine ablation (RAI) treatment – often performed to treat Graves’ disease and hyperthyroidism – can also cause hypothyroidism.
Thyroid patients should be advised of the risk of hypothyroidism after surgery or RAI, but there are situations where patients haven’t been aware of this possibility and become hypothyroid.
The takeaway is that if you have surgery to remove part of your thyroid gland or have RAI treatment for Graves’ or hyperthyroidism, you must monitor yourself carefully for signs of hypothyroidism. You should also have thyroid tests regularly to watch for any change in your thyroid function.
Radiation therapy to the head and neck area region can damage the thyroid gland and affect its function. The resulting hypothyroidism usually becomes evident within a year after treatment. Specifically:
- Radiation for head and neck cancer can frequently cause hypothyroidism as a late after-effect. Studies have shown that hypothyroidism is a frequent late effect after definitive radiotherapy for head and neck cancer.
- Radiation to the lower neck lymph nodes: Radiation therapy to the lymph nodes in the lower neck in breast cancer and lymphoma patients can also lead to hypothyroidism.
Some medications can interfere with the production or action of thyroid hormones, resulting in hypothyroidism. These include:
- Glucocorticoids, dopamine agonists, somatostatin analogs, and retinoids: These drugs inhibit TSH secretion.
- Lithium, tricyclic antidepressants, selective serotonin reuptake inhibitors (SSRIs), antiepileptics, rifampin, metformin, and amiodarone: These drugs mainly affect thyroid function directly
- Beta-blockers and corticosteroids: These drugs inhibit the conversion of T4 to T3 and interfere minimally with thyroid function test results
- Iodine-containing medications and supplements: These can exert hypothyroid effects through a phenomenon called the Wolff-Chaikoff effect, whereby ingesting a large dose of iodine shuts down thyroid hormone synthesis regardless of serum TSH levels. The most commonly prescribed of these medications is amiodarone, used to treat heart rhythm abnormalities like atrial fibrillation.
- Glucocorticoids: This drug class inhibits TRH secretion, decreasing serum TSH and thyroid function.
- Lithium: The drug lithium, used as a treatment for bipolar disorder, can trigger hypothyroidism in up to half of all patients on long-term therapy.
- Methimazole: Known by the brand name Tapazole, this antithyroid drug used to treat hyperthyroidism slows down thyroid production and can cause hypothyroidism.
The pituitary gland is a small gland in the brain that controls the secretion of thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to produce thyroid hormones. If the pituitary gland is damaged by a tumor, infection, head trauma, radiation, injury, or surgery, it may be unable to produce TSH – or fail to produce enough -- which can result in hypothyroidism.
Some women may develop hypothyroidism during or after pregnancy due to changes in the immune system or hormonal levels.
Inflammation of the thyroid, called thyroiditis, can also cause hypothyroidism. A bacterial or viral – and not autoimmune – thyroiditis can cause the thyroid to have fluctuations in function, resulting in an underactive thyroid and ongoing thyroid disease.
Working with an expert Paloma thyroid practitioner, you can determine the causes of your underactive thyroid and develop an effective plan for treatment and optimal health.
The first step in determining the underlying cause of your hypothyroidism is checking for thyroid antibodies. Paloma’s at-home testing kit makes a diagnostic blood test panel of thyroid hormone levels easy, convenient, and affordable.
You can schedule an appointment with one of Paloma’s qualified and knowledgeable thyroid care providers, who will work with you to identify the best thyroid hormone replacement and lifestyle treatment plan to help ensure relief of your hypothyroid symptoms, optimal thyroid function and levels of thyroid hormone, and overall wellness.