Types of hypothyroidism
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Types of Hypothyroidism: An Overview
Primary Hypothyroidism: Most Common Form
Primary hypothyroidism is the most prevalent type, accounting for over 99% of all cases. It occurs when the thyroid gland itself fails to produce sufficient thyroid hormones. Common causes include chronic lymphocytic thyroiditis (Hashimoto's disease), radioiodine thyroid ablation, thyroidectomy, high-dose head and neck radiation therapy, and certain medications like lithium and amiodarone1 4. This form is characterized by elevated thyroid-stimulating hormone (TSH) levels and low levels of thyroxine (T4)4.
Central Hypothyroidism: Pituitary or Hypothalamic Origin
Central hypothyroidism results from insufficient production of TSH due to disorders of the pituitary gland or hypothalamus. Causes include tumors, inflammatory conditions, infiltrative diseases, infections, pituitary surgery, and head trauma4. Unlike primary hypothyroidism, central hypothyroidism is marked by low T4 levels but normal or low TSH levels4.
Subclinical Hypothyroidism: Mild Thyroid Failure
Subclinical hypothyroidism is characterized by elevated TSH levels with normal free T4 levels. It is often asymptomatic but can progress to overt hypothyroidism. This condition is more prevalent in elderly populations and those with type 2 diabetes mellitus (T2DM) or metabolic syndrome (MetS)1 3 6. Subclinical hypothyroidism is associated with increased risks of cardiovascular diseases and diabetic complications3 6.
Consumptive Hypothyroidism: Rare and Severe
Consumptive hypothyroidism is a rare form caused by excessive inactivation of thyroid hormones due to high levels of type 3 iodothyronine deiodinase (D3) in tumors. This condition has been observed in both children and adults with vascular tumors, fibrous tumors, and gastrointestinal stromal tumors8 9. It requires high doses of thyroid hormone replacement and often tumor-directed therapy8 9.
Hypothyroidism in Childhood: Cretinism and Juvenile Myxedema
In children, hypothyroidism can manifest as cretinism, which can be sporadic or endemic. Sporadic cretinism is often due to developmental defects of the thyroid gland, while endemic cretinism is linked to iodine deficiency in goitrous families2 10. Juvenile myxedema is another term used to describe hypothyroidism in older children, often presenting with similar symptoms to adult hypothyroidism but with additional growth and developmental delays10.
Hashimoto Thyroiditis: Autoimmune Hypothyroidism
Hashimoto thyroiditis (HT) is the most common autoimmune cause of hypothyroidism. It includes several variants such as the fibrous variant, IgG4-related variant, juvenile form, Hashitoxicosis, and painless thyroiditis. HT is characterized by lymphocytic infiltration of the thyroid gland, leading to atrophy and hypothyroidism5. Diagnosis involves detecting antibodies against thyroid antigens and reduced thyroid echogenicity on ultrasound5.
Conclusion
Hypothyroidism encompasses a range of conditions from primary and central hypothyroidism to subclinical and consumptive forms. Each type has distinct etiologies, clinical features, and management strategies. Understanding these differences is crucial for accurate diagnosis and effective treatment.
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Most relevant research papers on this topic
Hypothyroidism: etiology, diagnosis, and management.
Hypothyroidism is caused by inadequate production or action of thyroid hormone in target tissues, and is treated with oral administration of synthetic thyroid hormone.
Highly CitedHypothyroidism as an inborn error of metabolism.
Hypothyroidism is an inborn error of metabolism, with three classic types: sporadic, athyroidic, and goitrogenic, with a third type occurring due to therapeutic use or accidental ingestion of substances with a goitrogenic action.
CASE FINDING FOR HYPOTHYROIDISM SHOULD INCLUDE TYPE 2 DIABETES AND METABOLIC SYNDROME PATIENTS: A LATIN AMERICAN THYROID SOCIETY (LATS) POSITION STATEMENT.
The Latin American Thyroid Society recommends aggressive case finding of hypothyroidism in both type 2 diabetes mellitus and metabolic syndrome patients, as thyroid function is affected in these conditions.
Systematic ReviewHypothyroidism
Hypothyroidism is a common condition affecting the thyroid gland, with primary causes being thyroid disease and central causes being pituitary or hypothalamic disorders.
Highly CitedHashimoto thyroiditis: clinical and diagnostic criteria.
Hashimoto thyroiditis is a complex and expanding autoimmune disease with various clinical variants and treatment focusing on synthetic thyroid hormones and surgery.
Highly CitedSubclinical Hypothyroidism and Type 2 Diabetes: A Systematic Review and Meta-Analysis
Type 2 diabetes mellitus (T2DM) is associated with a 1.93-fold increased risk of subclinical hypothyroidism and may increase diabetic complications.
Meta-Analysis
Rigorous JournalHighly CitedHypothyroidism
Hypothyroidism is a common condition with varying symptoms and can be life-threatening if untreated.
Rigorous JournalHighly CitedConsumptive hypothyroidism caused by paraneoplastic production of type 3 iodothyronine deiodinase.
Consumptive hypothyroidism can occur in nonvascular tumors, expanding the differential diagnosis and highlighting the need for targeted therapy in this rare syndrome.
Case ReportConsumptive Hypothyroidism: Case Report of Hepatic Hemangioendotheliomas Successfully Treated with Vincristine and Systematic Review of the Syndrome
Consumptive hypothyroidism syndrome (CHS) is a rare condition linked to hepatic vascular tumors, and prompt diagnosis and high-dose thyroid hormone replacement are crucial for optimal outcomes.
Systematic Review