The pituitary is a small gland located at the base of the brain. It has an important role in regulating the secretion of hormones from a number of glands, including the adrenal and thyroid glands. Some kinds of pituitary tumors can lead to the development of high blood glucose, resulting in diabetes.
Mechanism
A tumor in the pituitary gland can result in diabetes if the tumor secretes hormones, New York University's Langorne Medical Center explains. One of the hormones which is produced by the pituitary is known as adrenocorticotropin hormone, or ACTH. This hormone acts to stimulate the production of hormones by the adrenal cortex. The adrenal cortex secretes many different hormones including cortisol. Overproduction of cortisol by the adrenal cortex can lead to increased blood glucose levels, resulting in diabetes. Thus, by disrupting the body's hormonal balance, a pituitary tumor can result in diabetes.
Symptoms
Diabetes caused by a pituitary tumor can result in a number of symptoms. The high levels of glucose in the blood can overwhelm the kidneys, resulting in sugar appearing in the urine as well. The presence of sugar causes the kidneys to add extra liquid to the urine to try and dilute the sugar, resulting in the generation of large volumes of urine. The loss of liquid from excessive urination can also lead to persistent thirst and dehydration. Patients may also be persistently tired or fatigued as their body is unable to use glucose properly. Vision changes or blurred vision are also common symptoms of diabetes caused by a pituitary tumor.
Diagnosis
Diabetes can be diagnosed by measuring a patient's blood glucose level. A patient's blood glucose level is usually tested when she has not eaten for several hours, which is also known as a fasting blood glucose level. On the other hand, blood glucose testing is not sufficient to determine that the diabetes is caused by a pituitary tumor. There are two different ways to diagnose a pituitary tumor that is causing diabetes. The first is the use of a MRI scan that can show a mass in the pituitary. Blood tests can also be used, the Merck Manual explains. The level of ACTH can be measured; elevated ACTH levels suggest a pituitary tumor. The levels of cortisol in the blood can also be assessed. A follow-up test involves giving the patient dexamethasone, which is a synthetic form of cortisol. Patients with a pituitary tumor will not have as severe a drop in cortisol levels after dexamethasone testing compared to patients with a normally functioning pituitary.
Complications
Pituitary tumors that cause diabetes can also lead to a number of other symptoms due to the production of large amounts of cortisol. Patients may develop swelling of the face, gain weight around their trunk and develop a small clump of fat in between their shoulders. Other symptoms include a weakened immune system and the development of stretch marks. Large pituitary tumors can cause a number of problems, the Mayo Clinic explains. The pressure that the tumor generates on the brain can result in headaches and vision changes as well as fatigue, weakness and nausea. Pituitary tumors can also interfere with the production of a hormone that stimulates the thyroid, resulting in weight gain and intolerance to cold. This can also result in constipation and loss of body hair.
Treatment
The most common way of treating a pituitary tumor that is causing diabetes, Diabetes Monitor reports, is via surgical removal. This procedure is known as a transsphenoidal adenomectomy and involves gaining access to the pituitary through an incision made below the lip or nostril. If this procedure is unsuccessful, patients may have the tumor destroyed using radiation. Other treatment approaches include the use of mitotane, ketoconazole, trilostane, metyrapone and aminoglutethimide.
