Pituitary Gland : Hyperpituitarism (Overactive Pituitary Gland)
What is the pituitary gland?
The pituitary gland is a tiny pea-sized endocrine gland located in a bony cavity in the base of the brain. Endocrine glands secrete hormonal substances into the body’s bloodstream.
The pituitary gland plays a major role in regulating a wide range of biological functions. It secretes hormones involved in:
- Blood pressure
- Sexual maturation and function
Blood vessels connect the pituitary gland to a part of the brain known as the hypothalamus. The brain tells the pituitary to increase or decrease the secretion of certain hormones.
Sometimes the pituitary is called the “master gland” because it controls the activity of other endocrine glands. The pituitary gland consists of 3 parts: the anterior, intermediate, and posterior lobes.
The anterior lobe, which makes up about 80% of the gland, secretes these hormones:
- Adrenocorticotropic hormone (ACTH) causes the adrenal glands to produce steroid hormones, especially cortisol.
- Growth hormone (GH) regulates the body’s growth, metabolism, and composition.
- Thyroid stimulating hormone (TSH) causes the thyroid gland to produce hormones.
- Gonadotropins — luteinizing hormone (LH) and follicle stimulating hormone (FSH) — cause the ovaries and testes to secrete sex hormones involved in reproduction.
- Prolactin stimulates milk production in women who have given birth.
The intermediate lobe secretes only 1 hormone:
- Melanocyte-stimulating hormone affects skin pigmentation.
The posterior lobe stores and lets out 2 hormones that are produced by the hypothalamus:
- Antidiuretic hormone (ADH) regulates water and electrolyte balance.
- Oxytocin is involved in uterine contractions during childbirth and the production and release of breast milk.
What happens when the pituitary gland becomes overactive?
When the pituitary gland is overactive, it secretes excessive amounts of some hormones, usually due to the presence of a benign (noncancerous) tumor. Overactivity of the pituitary gland is called hyperpituitarism.
Several disorders related to an overactive pituitary gland can occur. These include:
Cushing’s syndrome (hypercortisolism): If the pituitary gland secretes too much ACTH, the adrenal glands may release too much cortisol. Cortisol regulates the metabolism of proteins, fats, and carbohydrates. It is also involved in the body’s inflammatory and immune responses. Symptoms of Cushing’s disease may include:
- Accumulation of fat in the upper body.
- Excessive facial hair in women.
- Pink or purplish stretch marks on the abdomen.
- Tendency to bruise easily.
- Bones may become fragile and tend to break more easily.
Acromegaly: This disorder is caused by secretion of excessive amounts of growth hormone (GH) in adults. Acromegaly can cause:
- Hands and feet to grow.
- Change in facial structure — jaw and brow may stick out and the nose, tongue, and lips may get bigger.
- Skin becoming thick, coarse, and oily.
- Irregular periods in women and erectile dysfunction in men.
- Increased risk for high blood pressure, diabetes, heart attack, and certain types of cancer.
In children and adolescents, excessive levels of growth hormone can result in a condition called gigantism. Children with this condition may have unusually long arms and legs and may grow to heights of 7 to 8 feet or more.
Prolactinoma: A tumor on the pituitary known as a prolactinoma may cause the gland to secrete too much prolactin. High levels of prolactin can disrupt normal reproductive functions in men and women by interfering with hormones produced by the testes and ovaries.
A prolactinoma can cause women who are not pregnant or nursing to experience tenderness of the breasts and start to produce breast milk (galactorrhea). Their menstrual periods may become irregular or might stop altogether. Women may become infertile or lose interest in having sex. Having intercourse may be painful due to vaginal dryness.
For men, the most common symptom of prolactinoma is erectile dysfunction. Men also may experience a decrease in or loss of sex drive, lower fertility, or loss of energy. In rare cases, men may secrete milk from their breasts or, when the prolactinoma is large, blindness or difficulty seeing can occur.
Hyperthyroidism: If the pituitary adenoma causes overproduction of thyroid stimulating hormone (TSH), the thyroid gland will become hyperactive. Symptoms may include:
- Rapid or irregular heartbeat.
- Weight loss.
- Muscular weakness.
How common is an overactive pituitary?
Small benign pituitary tumors (adenomas) are fairly common. They may be either secreting (releasing excess amounts of hormones) or non-secreting and do not cause any symptoms. Prolactinomas are the most common type of pituitary tumors, occurring in about 1 out of 10,000 people. They are more common in women than in men.
Acromegaly is a very rare disorder that occurs in only about 3 out of 1 million people each year. It generally is diagnosed in adults age 40 to 45.
Cushing’s syndrome is a relatively rare disorder that occurs mainly in adults from age 20 to 50 years old. When the syndrome is caused by an adenoma, it is about 5 times more common in women than in men.
Symptoms and Causes
What causes an overactive pituitary gland?
Benign tumors are the most frequent cause of an overactive pituitary. Generally it is not known why these tumors occur. Depending on which types of cells are affected, the pituitary gland will start to secrete excessive amounts of one or two hormones. In some cases, pituitary tumors may result from an inherited condition known as multiple endocrine neoplasia type 1(MEN1). This disorder also causes benign tumors of the pancreas and parathyroid glands. In rare cases, a cancerous tumor or a disorder of the hypothalamus may be the underlying cause.
Diagnosis and Tests
How is an overactive pituitary diagnosed?
Your doctor will ask you about your medical history and any symptoms you are having. He or she may order laboratory tests to measure the levels of hormones in your blood or urine. Various diagnostic tests will be performed depending on the underlying disorder that may be present.
- If a prolactinoma is suspected, tests will be performed to measure prolactin levels in the blood. Hypothyroidism (an underactive thyroid) can also cause elevated prolactin levels, so tests should be done to rule out this possibility.
- In the case of acromegaly, blood levels of growth hormone are usually elevated. GH levels can change over time because the pituitary gland secretes the hormone in spurts. Often an oral glucose tolerance test is performed to diagnose acromegaly. Healthy people experience a drop in blood GH levels after drinking glucose, unlike people with acromegaly.
- In the case of Cushing’s syndrome, tests may be ordered to rule out other causes, such as a tumor on the adrenal gland or the use of glucocorticoid drugs. Other tests include the high-dose dexamethasone suppression test and specialized blood sampling, in which a blood sample is taken from the veins of the sinuses that drain blood from the pituitary gland.
- If laboratory diagnostic tests suggest that a tumor is present, radiologic imaging tests will be performed to determine the size and location of the tumor. Usually magnetic resonance imaging (MRI) is more sensitive in this case than a computerized tomography (CAT) scan. CAT scans may be used with patients who cannot undergo MRI, such as those with pacemakers or other implants.
Management and Treatment
How is an overactive pituitary treated?
The treatment will depend on the underlying cause.
- Surgery: A procedure called a transsphenoidal adenomectomy is usually recommended for patients with acromegaly or Cushing’s disease. The surgeon makes a small incision through the nose or upper lip to reach the pituitary and remove the tumor. Although this procedure is very delicate, it has a success rate higher than 80% when performed by experienced surgeons. Transsphenoidal surgery is most effective for small tumors (under 10 mm in diameter). Potential drawbacks include long-term dependence on pituitary hormone replacement therapy and cerebrospinal fluid leakage.
- Medication: Drugs may be used to shrink large tumors before surgery or in cases where surgery is not an option. Medication to reduce prolactin levels is usually the preferred treatment for patients with a prolactinoma. Patients with acromegaly may be treated with drugs used to lower growth hormone levels and shrink tumors.
- Radiation: Radiation may be used to treat patients who cannot undergo surgery or who have some residual tumor tissue after surgery and do not respond to medication. There are two approaches to radiation, conventional and stereotactic therapies:
- Conventional radiation therapy is administered in small doses over a period of 4 to 6 weeks. One drawback is that radiation treatments can damage normal tissue surrounding the tumor.
- Stereotactic therapy provides a high-dose beam of radiation targeted at the tumor. It may be completed in one session, resulting in less damage to surrounding tissue. Most patients that undergo radiation treatment require hormone replacement therapy due to a gradual decline in the secretion of other pituitary hormones.