Endocrinology

Why Me? Exploring Hashimoto's and Other Causes

At a Glance

Hashimoto's disease is the most common cause of hypothyroidism, occurring when the immune system mistakenly attacks the thyroid gland. Other causes include surgical removal of the thyroid, radioactive iodine therapy, and rare issues with the pituitary gland.

While the symptoms of hypothyroidism are often the same, the reasons why the thyroid stops working can vary significantly. Understanding the “why” behind your diagnosis can help you and your doctor tailor your long-term care plan.

Hashimoto’s Disease: The Immune System’s Mistake

Hashimoto’s thyroiditis is the most common cause of hypothyroidism ^[1]. It is an autoimmune disorder, which means your immune system—specifically white blood cells called T-lymphocytes—mistakenly attacks your thyroid gland ^[2].

Over time, this constant attack leads to:

Inflammation and Infiltration: Immune cells invade the thyroid tissue ^[3].
Follicular Destruction: The tiny sacs in the thyroid that produce hormones are damaged ^[2].
Fibrosis: Healthy thyroid tissue is replaced by scar tissue, making the gland unable to produce enough hormone ^[3].

Why does it happen?

Research shows Hashimoto’s is triggered by a combination of factors:

Genetics: Specific genes (such as PTPN22) can make you more susceptible to autoimmune issues ^[4].
Environment and Nutrition: High iodine intake, low selenium levels, and Vitamin D deficiency have all been linked to the development or worsening of the disease ^[5]^[6]^[7].
Microbiome: The balance of bacteria in your gut may also play a role in how your immune system behaves toward your thyroid ^[5].

The “Autoimmune Cluster”

If you have Hashimoto’s, you are more likely to develop other autoimmune conditions because they often share the same genetic “pathways” ^[8]. Common associations include:

Celiac Disease: A sensitivity to gluten that can damage the small intestine ^[9].
Type 1 Diabetes: A condition where the body attacks insulin-producing cells ^[10].
Vitiligo: An autoimmune loss of skin pigment ^[11].

Iatrogenic Causes: Medical Treatments

Sometimes, hypothyroidism is a known and expected side effect of medical procedures, referred to as iatrogenic (caused by medical treatment).

Thyroidectomy: If your thyroid is surgically removed (due to cancer or nodules), hypothyroidism begins immediately after surgery ^[12].
Radioactive Iodine (RAI) Therapy: Often used to treat an overactive thyroid, RAI gradually destroys thyroid cells. Hypothyroidism typically develops within 2 to 3 months following this treatment ^[13].
External Radiation: Radiation therapy for cancers in the head or neck can damage the thyroid gland over time.

Primary vs. Secondary (Central) Hypothyroidism

It is important to distinguish where the problem originates:

Primary Hypothyroidism: The problem is in the thyroid gland itself (e.g., Hashimoto’s or surgery). TSH is usually high because the brain is screaming for more hormone that the thyroid can’t provide ^[14].
Secondary (Central) Hypothyroidism: This is rare and occurs when the pituitary gland or hypothalamus in the brain fails to tell the thyroid to work ^[15]. In these cases, TSH might be low or “normal,” but your actual thyroid hormone levels are still too low ^[16].

Congenital Hypothyroidism

Some infants are born with an underactive thyroid, known as congenital hypothyroidism ^[17]. This usually happens because the gland didn’t form correctly (dysgenesis) or because of a genetic “glitch” in how the hormone is manufactured (dyshormonogenesis) ^[14]. Because thyroid hormone is critical for brain development, newborn screening programs are used globally to detect and treat this immediately after birth ^[16].

Common questions in this guide

What is the most common cause of hypothyroidism?

The most common cause is Hashimoto's disease, an autoimmune disorder where your immune system mistakenly attacks your thyroid gland. Over time, this damages the gland and prevents it from producing enough hormones.

Are there other autoimmune diseases linked to Hashimoto's?

Yes, having Hashimoto's increases your likelihood of developing other autoimmune conditions because they share similar genetic pathways. Common related conditions include Celiac disease, Type 1 diabetes, and vitiligo.

Can medical treatments cause hypothyroidism?

Yes, this is known as iatrogenic hypothyroidism. It can occur immediately after the surgical removal of the thyroid or gradually following radioactive iodine therapy or external radiation to the head or neck.

What is the difference between primary and central hypothyroidism?

Primary hypothyroidism means the problem originates in the thyroid gland itself. Central, or secondary, hypothyroidism is a rare condition where the pituitary gland or hypothalamus in the brain fails to signal the thyroid to produce hormones.

Are babies ever born with hypothyroidism?

Yes, infants can be born with congenital hypothyroidism if the thyroid gland didn't form correctly or has a genetic defect. Newborn screening programs check for this immediately after birth to ensure early detection and treatment.

Curated prompts to bring to your next appointment.

1.Do my lab tests indicate that Hashimoto's is the cause of my hypothyroidism?
2.Given my Hashimoto's diagnosis, should I be screened for Celiac disease or other autoimmune conditions?
3.Are my selenium and Vitamin D levels within the optimal range for someone with thyroid autoimmunity?
4.Was my hypothyroidism caused by a problem with my thyroid gland (primary) or my pituitary gland (secondary/central)?
5.If I've had surgery or radiation, how often should we be testing my levels during this first year?

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References (17)

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2
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PMID: 35243857
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Unlocking the Therapeutic Potential: Selenium and Myo-Inositol Supplementation in Thyroid Disorders-Efficacy and Future Directions.
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Medicina (Kaunas, Lithuania) 2023; (59(5)) doi:10.3390/medicina59050853.
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Treatment of patients with Graves' disease and the appropriate extent of thyroidectomy.
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This page provides educational information about the causes of hypothyroidism, including Hashimoto's disease. Always consult your endocrinologist or primary care physician for an accurate diagnosis and personalized long-term care plan.

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