Table of ContentsView AllTable of ContentsSymptomsCausesDiagnosisTreatmentPrognosisFrequently Asked Questions
Table of ContentsView All
View All
Table of Contents
Symptoms
Causes
Diagnosis
Treatment
Prognosis
Frequently Asked Questions
Low thyroid levels can be due to failure of the thyroid gland itself (primary hypothyroidism) or failure of the pituitary gland (secondary hypothyroidism). Pituitary failure can manifest with several potential symptoms.
Read on to learn more about the symptoms, diagnosis, and treatment of secondary hypothyroidism.
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Secondary Hypothyroidism Symptoms
Thyroid hormonesare involved in many metabolic processes throughout the body. Symptoms of hypothyroidism generally include the following:
The symptoms listed above are common to primary and secondary hypothyroidism. Some additional symptoms are due to specific causes of pituitary failure (such as brain tumor) or due to low levels of other hormones. These symptoms can include:
Undiagnosed Hypothyroidism
What Causes Secondary Hypothyroidism?
The body functions best when hormone levels are maintained in the correct range. To accomplish this, the brain and endocrine organs work together through complex feedback loops.
The process starts in the part of the brain called thehypothalamus. Thehypothalamusreleases a hormone called thyrotropin-releasing hormone (TRH). This hormone signals the pituitary gland to releasethyrotropin, also known as thyroid-stimulating hormone (TSH).
TSH then signals the thyroid gland to release its own hormones,triiodothyronineandthyroxine(called T3 and T4 for short).T3 and T4 circulate in the blood and affect many biological processes, resulting in symptoms when levels are either too high or too low. The T3 and T4 then interact with the hypothalamus, telling it to secrete more or less thyrotropin-releasing hormone.
When any parts of the feedback loop are not functioning appropriately, thyroid levels can become either too high or too low, resulting in various symptoms. For example, pituitary failure results in inadequate TSH release, and subsequently low thyroid hormone (T3 and T4) levels.
Hormones Involved in Thyroid Regulation
The hormones involved in thyroid regulation include:
How Is Secondary Hypothyroidism Diagnosed?
Hypothyroidism is generally diagnosed withblood tests.Measuring low thyroid levels and circulating hormones can help determine where the problem is.
A low T3 and T4 and inappropriately low or normal TSH localizes the problem to the brain, either the pituitary gland or hypothalamus. Brain imaging is performed using magnetic resonance imaging (MRI) to evaluate for underlying causes and to rule out other possibilities.
When secondary hypothyroidism is diagnosed, evaluating other hormone systems, like cortisol, growth hormone, and sex hormones, is necessary,
Classification of HypothyroidismHypothyroidism can be classified according to which part of the feedback loop is affected, such as:Primary hypothyroidismoccurs when the thyroid gland does not release enough thyroid hormones.Secondary hypothyroidismoccurs when the pituitary gland does not release enough TSH.Tertiary hypothyroidismoccurs when the hypothalamus does not release enough thyrotropin-releasing hormone.
Classification of Hypothyroidism
Hypothyroidism can be classified according to which part of the feedback loop is affected, such as:Primary hypothyroidismoccurs when the thyroid gland does not release enough thyroid hormones.Secondary hypothyroidismoccurs when the pituitary gland does not release enough TSH.Tertiary hypothyroidismoccurs when the hypothalamus does not release enough thyrotropin-releasing hormone.
Hypothyroidism can be classified according to which part of the feedback loop is affected, such as:
Is Secondary Hypothyroidism Treatable?
Fortunately, hypothyroidism is treatable with medication.
Thyroid hormones can be replaced with a synthetic thyroid hormone calledlevothyroxine. Alternatively, desiccated thyroid hormone derived from thyroid glands of animals (known asArmour thyroid) can be administered. In secondary hypothyroidism, hormone levels are monitored to ensure appropriate dosing of thyroid hormone.
The underlying cause of secondary hypothyroidism also needs to be addressed. Pituitary tumors, one of the more common causes of secondary hypothyroidism, may requiresurgery.
Outlook for Secondary Hypothyroidism
While the management of hypothyroidism is straightforward and achievable with medication, the overall prognosis of secondary hypothyroidism is variable, depending on the underlying cause. Conditions like cancer, infection, head trauma, or bleeding need to be addressed to truly understand the overall prognosis.
Summary
Secondary hypothyroidism, also known as pituitary hypothyroidism, is a condition in which failure of the pituitary gland results in low thyroid stimulating hormone (TSH) and, subsequently, low thyroid hormone levels. Symptoms include fatigue, weight gain, constipation, menstrual irregularities, and skin, hair, and nail changes.
Diagnosing secondary hypothyroidism involves laboratory blood testing, and brain imaging is required to evaluate any underlying causes of pituitary failure. Hypothyroidism is treatable with medication, including synthetic thyroid hormones. The overall prognosis depends on the underlying cause.
A Word From Verywell
Because pituitary hypothyroidism is not common, achieving a diagnosis can be a stressful and complex experience. Know that low thyroid hormone disorders are treatable, though it can take time to start feeling better. Work with your healthcare provider to determine the appropriate dose of thyroid replacement medication so you can feel better sooner.
Frequently Asked QuestionsThe pituitary gland is responsible for secreting hormones that interact with the kidneys, sex glands, adrenal glands, and thyroid gland. With pituitary gland failure, symptoms include fatigue, low blood pressure, irregular or absent menstrual cycles, infertility, decreased libido, mood changes, weight changes, muscle weakness, and skin, hair, and nail changes.In primary hypothyroidism, a problem involving the thyroid gland itself, the pituitary gland can become enlarged due to enlargement (hyperplasia) of cells that secrete thyroid stimulating hormone (TSH).This is because there is excess thyrotropin stimulating hormone, which tells the pituitary gland to secrete TSH to normalize thyroid levels.Pituitary hypothyroidism is diagnosed using laboratory tests for thyroid hormone levels (T3 and T4) as well as thyroid stimulating hormone (TSH) levels. Low T3 and T4 levels with normal or low TSH levels indicate a problem with the brain. A brain MRI is needed for further evaluation.
The pituitary gland is responsible for secreting hormones that interact with the kidneys, sex glands, adrenal glands, and thyroid gland. With pituitary gland failure, symptoms include fatigue, low blood pressure, irregular or absent menstrual cycles, infertility, decreased libido, mood changes, weight changes, muscle weakness, and skin, hair, and nail changes.
In primary hypothyroidism, a problem involving the thyroid gland itself, the pituitary gland can become enlarged due to enlargement (hyperplasia) of cells that secrete thyroid stimulating hormone (TSH).This is because there is excess thyrotropin stimulating hormone, which tells the pituitary gland to secrete TSH to normalize thyroid levels.
Pituitary hypothyroidism is diagnosed using laboratory tests for thyroid hormone levels (T3 and T4) as well as thyroid stimulating hormone (TSH) levels. Low T3 and T4 levels with normal or low TSH levels indicate a problem with the brain. A brain MRI is needed for further evaluation.
8 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Thyroid Association.Hypothyroidism.Endocrine Society.Hypopituitarism.Mohamed MFH, Danjuma M, Mohammed M, et al.Myxedema psychosis: Systematic review and pooled analysis.Neuropsychiatr Dis Treat. 2021;17. doi:10.2147/NDT.S318651Endocrine Society.Endocrine facts and figures: thyroid.Endocrine Society.Thyroid and parathyroid hormones.American Thyroid Association.Thyroid function tests.American Thyroid Association.Thyroid hormone treatment.Shukla P, Bulsara KR, Luthra P.Pituitary hyperplasia in severe primary hypothyroidism: a case report and review of the literature.Case Rep Endocrinol. 2019;2019:2012546. doi:10.1155/2019/2012546
8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Thyroid Association.Hypothyroidism.Endocrine Society.Hypopituitarism.Mohamed MFH, Danjuma M, Mohammed M, et al.Myxedema psychosis: Systematic review and pooled analysis.Neuropsychiatr Dis Treat. 2021;17. doi:10.2147/NDT.S318651Endocrine Society.Endocrine facts and figures: thyroid.Endocrine Society.Thyroid and parathyroid hormones.American Thyroid Association.Thyroid function tests.American Thyroid Association.Thyroid hormone treatment.Shukla P, Bulsara KR, Luthra P.Pituitary hyperplasia in severe primary hypothyroidism: a case report and review of the literature.Case Rep Endocrinol. 2019;2019:2012546. doi:10.1155/2019/2012546
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Thyroid Association.Hypothyroidism.Endocrine Society.Hypopituitarism.Mohamed MFH, Danjuma M, Mohammed M, et al.Myxedema psychosis: Systematic review and pooled analysis.Neuropsychiatr Dis Treat. 2021;17. doi:10.2147/NDT.S318651Endocrine Society.Endocrine facts and figures: thyroid.Endocrine Society.Thyroid and parathyroid hormones.American Thyroid Association.Thyroid function tests.American Thyroid Association.Thyroid hormone treatment.Shukla P, Bulsara KR, Luthra P.Pituitary hyperplasia in severe primary hypothyroidism: a case report and review of the literature.Case Rep Endocrinol. 2019;2019:2012546. doi:10.1155/2019/2012546
American Thyroid Association.Hypothyroidism.
Endocrine Society.Hypopituitarism.
Mohamed MFH, Danjuma M, Mohammed M, et al.Myxedema psychosis: Systematic review and pooled analysis.Neuropsychiatr Dis Treat. 2021;17. doi:10.2147/NDT.S318651
Endocrine Society.Endocrine facts and figures: thyroid.
Endocrine Society.Thyroid and parathyroid hormones.
American Thyroid Association.Thyroid function tests.
American Thyroid Association.Thyroid hormone treatment.
Shukla P, Bulsara KR, Luthra P.Pituitary hyperplasia in severe primary hypothyroidism: a case report and review of the literature.Case Rep Endocrinol. 2019;2019:2012546. doi:10.1155/2019/2012546
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