Pituitary hypothyroidism is when your pituitary gland doesn’t produce enough hormones to stimulate the production of a normal amount of thyroid hormone.

The medical term for this condition is secondary hypothyroidism, or central hypothyroidism.

Three different glands play a role in the production of your two thyroid hormones, triiodothyronine (T3) and thyroxine (T4):

  • A brain structure called the hypothalamus produces thyrotropin-releasing hormone (TRH).
  • TRH stimulates your pituitary gland, a small gland located at the bottom of the brain, to release thyroid-stimulating hormone (TSH).
  • TSH stimulates your thyroid gland, which is located in the front of the neck, to produce T3 and T4.

A problem with any of these three glands can lead to hypothyroidism. The vast majority of hypothyroidism diagnoses are caused by problems with the thyroid gland and are categorized as primary hypothyroidism.

A small number of people with low thyroid have a problem with their pituitary gland. Their bodies do not produce enough TSH. When this happens, it’s referred to as secondary hypothyroidism.

Read on to learn more about secondary hypothyroidism, including what causes it and how it’s different from primary hypothyroidism.

Vs. primary and tertiary hypothyroidism

Hypothyroidism is very common and affects about 5% of Americans ages 12 years and older. It’s often mild and either does not cause symptoms or causes very mild symptoms. It’s about 8 to 9 times more common in women than men.

About 99% of hypothyroidism cases are primary hypothyroidism, where a problem with your thyroid gland causes it to produce an inadequate amount of thyroid hormone. Primary hypothyroidism is most commonly caused by Hashimoto’s disease, a condition that develops when your immune system attacks healthy cells in your thyroid.

Secondary and tertiary hypothyroidism are collectively known as central hypothyroidism.

  • Secondary hypothyroidism occurs when a problem with your pituitary gland causes it to produce inadequate amounts of TSH.
  • Tertiary hypothyroidism occurs when your hypothalamus does not produce enough TRH.

Pituitary hypothyroidism is caused by problems with your pituitary gland. These problems can be present at birth or acquired throughout your life.

Potential causes of secondary hypothyroidism include:

  • pituitary tumors
  • Sheehan syndrome, a rare condition where extreme blood loss during childbirth damages your pituitary gland
  • TRH resistance, which is when cells in your pituitary gland have a weak response to TRH
  • lymphocytic hypophysitis, which is a rare pituitary autoimmune condition
  • radiation therapy to the brain
  • some drugs like opioids, prednisone, and dopamine
  • head trauma
  • infectious diseases like syphilis or tuberculosis

In adults, secondary hypothyroidism is often caused by a noncancerous pituitary tumor called macroadenoma.

Although hypothyroidism in general is much more common in people assigned female at birth, central hypothyroidism seems to affect everyone roughly equally. It can affect people of all ages.

The estimated prevalence of central hypothyroidism at birth is 1 in 16,000 to 1 in 100,000.

Symptoms of pituitary hypothyroidism can range from mild and barely noticeable to severe. When present from birth, symptoms usually start in infancy but can rarely be delayed until adulthood.

Typical symptoms of hypothyroidism include:

In babies, central hypothyroidism may cause symptoms like:

It’s important to see a doctor if you have potential symptoms of hypothyroidism without an obvious cause. Hypothyroidism is usually treatable with medication.

People who delay getting proper treatment may develop late symptoms of hypothyroidism. Late symptoms can include:

To diagnose pituitary hypothyroidism, a doctor will likely start by asking about your symptoms and reviewing your personal and family medical history. They may perform a physical exam where they feel your thyroid gland for abnormal changes.

Doctors can confirm that you have secondary hypothyroidism with a blood test. If you have secondary hypothyroidism, your blood test will reveal low thyroid hormone levels as well as low TSH levels.

Treating pituitary hypothyroidism usually involves taking medication to replace your body’s natural production of the thyroid hormone thyroxin. The first-line treatment is usually levothyroxine for primary, secondary, and tertiary hypothyroidism. The dose your doctor prescribes depends on factors like:

  • your age
  • your body weight
  • whether you have other health conditions

You will likely need to take levothyroxine long term.

Pituitary gland dysfunction can also cause problems with other hormone levels, which may require separate treatment.

For example, some people may also have secondary adrenal insufficiency that may require glucocorticoid treatment. Secondary adrenal insufficiency is when your pituitary gland does not produce enough adrenocorticotropic hormone (ACTH), which leads to low cortisol levels.

Surgery may be needed to treat brain tumors to prevent them from continuing to grow and cause additional complications.

Most people can live a typical life with medication treatment to correct thyroid deficiency.

In very rare cases, hypothyroidism can progress to myxedema. This is a severe form of hypothyroidism that has a mortality rate of 20% to 60%. It’s estimated to affect about 1 in 4.5 million people.

Hypothyroidism can negatively affect proper brain growth and development in infants. Early detection and treatment are essential in helping prevent brain damage.

Secondary hypothyroidism is a rare form of hypothyroidism caused by your pituitary gland underproducing TSH. It makes up less than 1% of cases of hypothyroidism and can cause symptoms like fatigue, poor cold tolerance, and weight gain.

Secondary hypothyroidism can occur at birth or be acquired later in life. A doctor can help you determine which type of hypothyroidism you have by testing your thyroid hormone and TSH levels.