Difference Between Overt Hypothyroidism Vs Subclinical Hyperthyroidism

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Difference between Overt Hypothyroidism vs Subclinical Hyperthyroidism: When thyroid hormones, particularly T4 and T3, are deficient, the body slows down, which is known as Overt Hypothyroidism. It usually manifests as weariness, weight gain, and cold intolerance, with high TSH levels serving as a defining feature. Conversely, Subclinical Hyperthyroidism is characterized by low TSH levels combined with normal T3 and T4 levels, and it frequently shows only weak symptoms or no symptoms at all. Subclinical Hyperthyroidism may require monitoring because it may evolve into Overt Hyperthyroidism or because of the related health risks, especially in older people. Overt Hypothyroidism requires treatment to restore hormone levels.

Difference between Overt Hypothyroidism and Subclinical Hyperthyroidism

Reduced thyroid function, increased TSH levels, and noticeable symptoms including weight gain and exhaustion are the hallmarks of Overt Hypothyroidism. On the other hand, Subclinical Hyperthyroidism typically remains asymptomatic or manifests moderately in the form of palpitations, with slightly enhanced thyroid function and normal to moderately suppressed TSH levels. The table below provides the differences between Overt Hypothyroidism and Subclinical Hyperthyroidism.


Overt Hypothyroidism

Subclinical Hyperthyroidism

Thyroid Function

Decreased thyroid function

Slightly elevated thyroid function

TSH Levels

Elevated thyroid-stimulating hormone (TSH) levels

Normal to slightly suppressed TSH levels

Free Thyroxine (FT4)

Decreased levels

Normal levels


Pronounced symptoms such as fatigue, weight gain, cold intolerance

Often asymptomatic or mild symptoms like palpitations, anxiety

Risk of Complications

Higher risk of complications such as cardiovascular disease, infertility, mental health issues

Lower risk of complications compared to overt hyperthyroidism


Typically requires thyroid hormone replacement therapy

May not require immediate treatment, often monitored closely before intervention

Cardiovascular Effects

Increased risk of high blood pressure, elevated cholesterol levels, and heart disease

May have mild cardiovascular effects such as increased heart rate

Bone Health

Higher risk of osteoporosis due to decreased thyroid hormone levels affecting bone density

Generally not associated with significant impact on bone health unless prolonged or severe

Fertility and Menstrual Irregularities

Menstrual irregularities, difficulty conceiving, and increased risk of miscarriage

May have mild menstrual irregularities or fertility issues in severe cases

Neurological Effects

May experience cognitive impairment, depression, and slowed reflexes

Less likely to experience neurological symptoms unless thyroid levels become severely imbalanced

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What is Overt Hypothyroidism?

When the thyroid gland doesn't generate enough hormones, it can cause Overt Hypothyroidism, which raises TSH levels and causes symptoms like weight gain, lethargy, and cold intolerance. Hormone replacement therapy is a common treatment method.

Causes of Overt Hypothyroidism 

  • Autoimmune Thyroiditis (Hashimoto's Thyroiditis): This is the most common cause of Hypothyroidism in iodine-sufficient regions. It happens when the thyroid gland is unintentionally attacked by the immune system, which causes inflammation and finally thyroid tissue death.
  • Thyroidectomy or Radioiodine Therapy: If too much thyroid tissue is removed or destroyed during thyroid cancer treatment or other surgical procedures involving the removal of the thyroid gland, the patient may develop Hypothyroidism.
  • Iodine Deficiency: Iodine is a necessary mineral that is needed for the production of thyroid hormones. When iodine intake is low, the body may not have the raw materials needed to produce thyroid hormone, which can lead to Hypothyroidism.
  • Congenital Hypothyroidism: Hypothyroidism can occur at birth in certain babies due to underdeveloped or non-functioning thyroid glands. If treatment for this illness is not received, it may lead to developmental delays and other health problems.
  • Medication: Several drugs, including amiodarone, lithium, tyrosine kinase inhibitors, and interferon-alpha, can interfere with the thyroid's ability to produce or function thyroid hormones, which can result in Hypothyroidism.
  • Pituitary or Hypothalamic Dysfunction: Conditions affecting the pituitary gland or hypothalamus, which release Thyroid-Stimulating Hormone (TSH) and Thyrotropin-Releasing Hormone (TRH), respectively, are responsible for controlling the production of thyroid hormone and can cause Hypothyroidism. 

Symptoms of Overt Hypothyroidism 

  • Fatigue: A classic sign of Hypothyroidism is feeling too tired, even after getting enough sleep.
  • Weight Gain: An unexpected weight increase or trouble decreasing weight even when following a balanced diet and activity schedule.
  • Cold Intolerance: Experiencing exceptionally high levels of sensitivity to cold, even in settings that other people find pleasant.
  • Constipation: Reduced bowel motions and slowed digestion can cause constipation.
  • Dry Skin and Hair: The hair may become brittle, coarse, and prone to breaking, while the skin may become dry, rough, and pale. It's also possible to have hair thinning or loss, especially around the eyebrows and scalp.
  • Joint Pain and Weakness: It's possible to have joint pain or stiffness along with weakness in the arms and legs. 

What is Subclinical Hyperthyroidism?

Low amounts of Thyroid-Stimulating Hormone (TSH) coexisting with normal levels of thyroid hormones T3 and T4 are known as Subclinical Hyperthyroidism. It is frequently undetected during regular blood tests and is asymptomatic. Thyroiditis, poisonous nodular goiter, autoimmune diseases such as Graves' disease, excessive thyroid hormone replacement therapy, and certain drugs are some of the possible causes. Even though therapy might not be required right away, routine medical monitoring is crucial to determining whether Overt Hyperthyroidism or its consequences will progress and need treatment.

Causes of Subclinical Hyperthyroidism

  • Graves' Disease: Graves' disease is an autoimmune disorder in which the immune system mistakenly attacks the thyroid gland, causing it to produce an excess of thyroid hormone.
  • Toxic Nodular Goiter: This disorder is characterized by the development of one or more nodules in the thyroid gland that produce excess thyroid hormone in the absence of TSH control.
  • Thyroiditis: Thyroid gland inflammation that results in the release of thyroid hormone into the bloodstream. It can be brought on by infections, autoimmune disorders, or other conditions. 
  • Overuse of Thyroid Hormone Replacement Therapy: Patients receiving treatment for hypothyroidism may unintentionally take too much medication, which can result in Subclinical Hyperthyroidism.
  • Usage of Specific Drugs or Supplements: Subclinical Hyperthyroidism is a side effect of using particular drugs and supplements, such as amiodarone, thyroid hormone supplements, and iodine-containing drugs.
  • TSH-Secreting Pituitary Adenoma: An uncommon kind of pituitary tumor that secretes too much TSH, stimulating the thyroid gland and causing it to create thyroid hormones. 

Symptoms of Subclinical Hyperthyroidism

  • Increased Heart Rate (Tachycardia): Even when at rest, people may notice that their heart is pumping more quickly than usual.
  • Palpitations: Feelings of fast or erratic heartbeats, which can resemble pounding or fluttering in the chest.
  • Unexplained Weight Loss: People may lose weight accidentally even when they don't alter their diet or level of physical activity.
  • Heat Intolerance: Even at pleasant temperatures, feeling overly warm or perspiring more than normal.
  • Anxiety or Nervousness: Some people may have increased jitters or anxiety.
  • Tremors: Tiny tremors in the hands or fingers may happen, and on occasion, these tremors may be apparent to others.
  • Increased Hunger: Although this symptom is less prevalent, some people may still have an increased appetite even after losing weight. 

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Similarities between Overt Hypothyroidism and Subclinical Hyperthyroidism

  • Presentation without Symptoms: In the early phases of both Subclinical Hyperthyroidism and Overt Hypothyroidism, symptoms may not be evident. Frequently, they are unintentionally found while doing standard blood work or diagnosing other illnesses.
  • Prospective Progression: Although Overt Hypothyroidism and Subclinical Hyperthyroidism may not always lead to Overt Hypothyroidism or vice versa, both disorders can worsen thyroid dysfunction if left unchecked or uncontrolled.
  • Elevated Risk of Cardiovascular Complications: Heart disease, high blood pressure, and arrhythmias have all been linked to elevated risks of cardiovascular complications in both Overt Hypothyroidism and Subclinical Hyperthyroidism.

In summary, Overt Hypothyroidism and Subclinical Hyperthyroidism are two distinct thyroid disorders that vary in hormone levels and symptom intensity. Low TSH levels, along with normal thyroid hormone levels, define Subclinical Hyperthyroidism, which can manifest with mild to no symptoms. Low thyroid hormones and elevated TSH levels cause Overt Hypothyroidism, which manifests as symptoms. Both illnesses require close management and monitoring to prevent complications and maintain good health, despite the differences in available treatments.

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What is Overt Hypothyroidism?

Underactive thyroid function results in low thyroid hormone (T3 and T4) and High Thyroid-Stimulating Hormone (TSH) levels, which is the hallmark of overt hypothyroidism. Notable side effects include weight gain, exhaustion, and cold sensitivity.

What causes Overt Hypothyroidism?

Hashimoto's thyroiditis, or autoimmune thyroiditis, is the most prevalent cause of Overt Hypothyroidism. In this condition, the thyroid gland is attacked by the immune system. Iodine deficiency, thyroid surgery, radiation therapy, and specific drugs are some more causes.

What are the symptoms of Overt Hypothyroidism?

Overt Hypothyroidism manifests as weariness, weight gain, constipation, dry skin, hair loss, and intolerance to colds. Menstrual abnormalities, sadness, and muscle weakness are some possible symptoms.

What is Subclinical Hyperthyroidism?

Low levels of Thyroid-Stimulating Hormone (TSH) along with normal levels of thyroid hormones (T3 and T4) are the hallmarks of Subclinical Hyperthyroidism. This suggests a modest case of hyperthyroidism, in which the thyroid gland secretes a little bit more hormone than is required.

What causes Subclinical Hyperthyroidism?

The most prevalent autoimmune cause of Subclinical Hyperthyroidism is Graves' disease. Thyroiditis, toxic nodular goiter, high iodine consumption, and specific drugs are some more causes.

What are the symptoms of Subclinical Hyperthyroidism?

Subclinical Hyperthyroidism frequently exhibits no symptoms at all or only minor ones like anxiety, palpitations, heat sensitivity, and weight loss. However, many people could not even show any symptoms.

What are the similarities between Overt Hypothyroidism and Subclinical Hyperthyroidism?

Both disorders are associated with dysregulation of thyroid hormones; Overt Hypothyroidism is typified by low levels of thyroid hormone and increased TSH, whereas Subclinical Hyperthyroidism has low TSH levels but normal thyroid hormone levels.

What are the differences between Overt Hypothyroidism and Subclinical Hyperthyroidism?

Overt Hypothyroidism is characterized by low thyroid hormone levels and raised TSH, which cause apparent symptoms, whereas Subclinical Hyperthyroidism is characterized by low TSH levels despite adequate thyroid hormone levels, which frequently go unnoticed.