The pituitary gland is at the helm of the endocrine system and impacts everything from a woman's monthly menstrual cycle to one's ability to handle stress. This pea-sized gland, which is nestled at the base of the brain, is responsible for the secretion of several hormones that, in turn, trigger the release of other hormones. When the pituitary gland is diseased, the entire endocrine system is potentially affected.
Sometimes, the pituitary gland may become underactive, causing a condition called hypopituitarism. This condition affects the anterior (front) lobe of the pituitary gland, which results in partial or complete loss of functioning in that lobe. As a result, the pituitary loses its ability to produce certain hormones. Symptoms of hypopituitarism will vary depending on which hormones are affected. The symptoms may develop slowly and gradually, or occur suddenly from seemingly out of nowhere.
Pituitary tumors are extremely common. Studies have found that benign tumors in the pituitary gland are present in about 25 percent of the population. To figure out the scope and significance of these benign brain tumors, Congress passed the Benign Brain Tumor Cancer Registries Amendment Act in October 2002. The law forces hospitals, clinics, and doctors to report pituitary tumor incidence rates in their cancer registries.
When hypopituitarism affects the pituitary's production of TSH, you may develop central hypothyroidism. Symptoms of central hypothyroidism are similar to those in hypothyroidism — you may experience weight gain, fatigue, depression, forgetfulness, and sensitivity to the cold.
Like hypothyroidism, central hypothyroidism can be difficult to diagnose. Despite the presence of symptoms, TSH levels are often in the low normal range. A more accurate measure may be free T4 levels, which are often low in people with central hypothyroidism. Doctors also rely on symptoms reported by the patient, which lead to testing for a deficit in several pituitary hormones.
The thyroid gland isn't the only gland that can be affected by hypopituitarism. Pituitary dysfunction may also cause a reduction in the production of several other hormones:
Growth Hormone (GH)
GH controls bone and tissue growth and maintains the appropriate balance of muscle and fat tissue. In adults, the lack of GH can cause fatigue, poor physical and mental function, and muscle weakness. In children, insufficient GH can stunt growth.
Luteinizing Hormone (LH)
LH regulates the menstrual cycle in women and stimulates testosterone production in men. Without enough of it, women may stop menstruating, become infertile, and experience vaginal dryness. In men, LH stimulates the production of testosterone, a hormone responsible for masculinization and libido. Without adequate LH, they experience erectile dysfunction.
Follicle-Stimulating Hormone (FSH)
FSH controls sperm production in men and ovulation in women. A deficiency causes a decrease in sperm production that can cause infertility.
Adrenocorticotropic Hormone (ACTH)
ACTH stimulates the adrenal glands to produce cortisol, the major stress hormone. Without it, you may experience weight loss, fatigue, depression, nausea, and vomiting.
Antidiuretic Hormone (ADH)
ADH regulates urine production and maintains water balance in your body. Inadequate amounts of ADH can cause diabetes insipidus, a condition characterized by excessive urination and thirst.
Prolactin regulates the development of female breasts, as well as the production of breast milk in nursing moms. Insufficient prolactin can make it hard for new moms to nurse.
As hypopituitarism gradually worsens, the number of hormones affected can increase, too, causing more symptoms. The hormones that are affected seem to follow a predictable pattern. The first hormone involved is usually GH, followed by LH and FSH, then TSH, and finally ACTH.
Many factors can trigger hypopituitarism. Causes include tumors, radiation, brain surgery, inadequate blood supply to the pituitary, infection, or head trauma. In some cases, the cause of hypopituitarism is an indirect problem with the hypothalamus, such as a tumor, TB, or sarcoidosis, an autoimmune disease that causes inflammation in the lungs and/or lymph nodes.