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Have you heard of the term central hypothyroidism? And how is it different from “hypothyroidism” in general? Central hypothyroidism -- also known as secondary hypothyroidism or tertiary hypothyroidism -- is a type of hypothyroidism, which is a condition of low thyroid hormone. Central hypothyroidism is less common than other forms of hypothyroidism. But, it is important to understand what it is and how it differs from primary hypothyroidism.

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Before we jump into central hypothyroidism, let’s briefly review how a normal thyroid gland functions.

The thyroid is a butterfly-shaped gland located at the bottom of your neck. Its primary role is to make and release thyroid hormones - thyroxine (T4) and triiodothyronine (T3). These hormones help regulate your metabolism (energy levels), growth and development. Nearly every cell in the body needs thyroid hormone to function correctly.

Thyroid hormone production is regulated by a complex feedback loop known as the hypothalamus-pituitary-thyroid (HPT) axis. Here’s how it works:

The cycle begins in the hypothalamus, which is part of the brain. When the hypothalamus senses low thyroid hormone levels, it secretes thyrotropin-releasing hormone (TRH). This hormone travels to the pituitary gland, also located in the brain. Once here, TRH tells the pituitary to release a pituitary hormone known as thyroid-stimulating hormone (TSH). TSH then travels down to the thyroid gland.

Upon receiving the signal from TSH, your thyroid will release T4 and T3. Your pituitary gland will continue to release TSH until your thyroid hormone level reaches a specific level in the blood. When that level is reached, your hypothalamus stops releasing TRH, thus suppressing TSH and thyroid hormone production. As your cells use up the thyroid hormone and levels drop, this signals the hypothalamus to release TRH. And as you can guess, the cycle continues.

This cycle occurs throughout the day and night. Your body adjusts thyroid hormone production based on its needs. For instance, thyroid hormone needs will be higher during pregnancy or periods of physical activity and lower during times of rest.

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Hypothyroidism is the broad term for a condition where you have low levels of thyroid hormone. It results from an underactive thyroid or partially or fully removed thyroid gland. The cause of the hypothyroidism varies, however. Over 95% of those with hypothyroidism will have primary hypothyroidism.

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Primary hypothyroidism

In primary hypothyroidism, the thyroid gland cannot produce enough thyroid hormone to meet the body’s needs. This is often due to damage or destruction of the thyroid cells. Hashimoto’s thyroiditis, a thyroid autoimmune disorder, is the most common cause of primary hypothyroidism in the United States.

Other causes of primary hypothyroidism include:

• Thyroid removal as part of a treatment plan for Graves’ disease or thyroid cancer
• Radiotherapy for head and neck cancer
• Exposure to chemicals and drugs
• Medications such as amiodarone and lithium
• Iodine deficiency
• Congenital hypothyroidism at birth

Since thyroid hormone levels are low, TRH and TSH will continually be secreted from the different areas of the brain. However, damage to the thyroid cells prevents them from producing thyroid hormone. Thus, thyroid levels never reach a normal level in the blood. Because of this, nothing signals the brain to turn off the production of TRH and TSH. Therefore, those with primary hypothyroidism present with high TSH levels and low levels of actual thyroid hormones.

Now, with a better understanding of the most common form of hypothyroidism, let’s see what sets central hypothyroidism apart.

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Central hypothyroidism

Central hypothyroidism is rare, accounting for less than 1% of all cases of hypothyroidism. It can affect people of all ages.

Unlike primary hypothyroidism, central hypothyroidism results from dysfunction in the pituitary gland or hypothalamus. Remember, these parts of the brain release signaling hormones that ultimately stimulate thyroid production. When signaling hormones don’t reach the thyroid, the thyroid doesn’t know how to release more thyroid hormones.

Those with central hypothyroidism -- sometimes called hypothalamic hypothyroidism -- may have a low TRH level if the hypothalamus is affected or an underactive pituitary gland, limiting the amount of TSH being released. In both cases, the HPT axis is interrupted, resulting in hypothyroidism. Central hypothyroidism may cause a drop in TSH, but the TSH level may stay within a normal range. Same with T4 levels - it may be low or within a normal range.

So, in central hypothyroidism, your thyroid works fine; it just isn’t receiving the signals to make and release thyroid hormone. Head trauma or injury, brain tumors, and certain autoimmune disorders, amongst other causes, can cause central hypothyroidism.

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Optimizing your thyroid levels with thyroid hormone replacement medication is usually the first step in minimizing symptoms.

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Your hypothalamus and pituitary secrete many hormones, not just ones related to the HPT axis. So, suppose there is dysfunction in these areas. In that case, symptoms can vary based on the underlying cause or area affected. This can make it hard for hypothyroid patients and their doctors to determine which symptoms are related to hypothyroidism. For instance, a pituitary tumor can cause vision problems and alter different hormone levels, causing symptoms that can overlap with hypothyroidism.

Central hypothyroidism shares many symptoms with primary hypothyroidism. Common symptoms of hypothyroidism include

Fatigue: You might feel tired all the time, even after a good night’s sleep.

Weight gain: Hypothyroidism can cause unexplained weight gain despite eating a healthy diet and maintaining an exercise routine. You may also find it hard to lose weight.

Cold intolerance: You may feel cold, even in mild temperatures. This is because your cells slow down when they don’t have enough thyroid hormone. And slower cells mean less heat production.

Cognitive impairment/brain fog: Trouble concentrating, memory lapses, and feeling like you can’t think clearly are common cognitive symptoms of hypothyroidism. This group of symptoms is often referred to as brain fog.

Menstrual disorders: Those assigned female at birth might have changes in their menstrual cycle, including irregular periods or heavier-than-usual bleeding. Menstrual irregularities may lead to problems getting pregnant.

Dry skin and hair: Central hypothyroidism can lead to dry, flaky skin and brittle hair and nails. Some may even experience hair loss.

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An accurate diagnosis of central hypothyroidism involves a combination of clinical evaluation, thorough medical history, and thyroid function tests. Your healthcare provider will likely test your thyroid function by measuring the levels of your thyroid biomarkers—TSH, T3, and T4. However, changes in thyroid biomarkers aren’t as pronounced in primary hypothyroidism. This can make it more complicated to get an accurate diagnosis of central hypothyroidism. Your provider may order more tests or follow your thyroid biomarkers over time.

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If you’re diagnosed with central hypothyroidism, your healthcare provider will work with you to develop a personalized treatment plan. The primary treatment goal is to restore thyroid hormone levels to normal. Here’s how:

• Thyroid hormone replacement medication: All thyroid hormone replacement medications restore thyroid hormone levels in your body. The most common medication prescribed is a daily dose of levothyroxine, a synthetic form of T4. Other thyroid hormone replacement supplements include liothyronine (Cytomel) and natural desiccated thyroid (NDT) (Armour Thyroid, NP Thyroid). Liothyronine only contains synthetic T3, while desiccated thyroid contains natural forms of both T4 and T3.
• Monitoring and titration: Your healthcare provider will evaluate your thyroid function test results. They will change your medication dosage based on your levels. You may need to increase your thyroid hormone medication dose during pregnancy or if you take a synthetic form of estrogen, such as birth control pills or estrogen replacement therapy. You may need to decrease your dose if you lose weight, are postpartum, or have heart problems.

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Living with central hypothyroidism requires ongoing management and communication with your thyroid healthcare team. Regular check-ups and blood tests help ensure your thyroid hormone levels remain within the optimal range.

Here at Paloma Health, we offer comprehensive care for those with hypothyroidism. Our services include

• Online video visits with one of our thyroid experts
• Prescription and lab monitoring with our convenient at-home thyroid testing kit
• Personalized care plans for your thyroid journey
• Symptom tracking

Want to learn more about our services? Schedule a free consultation call today to learn about our membership and whether Paloma may be a good fit for you.