Cushing's disease is a hormonal disorder. In this syndrome, there are excessive amounts of the hormone cortisol in the body. Cortisol is made in the adrenal glands and is released in response to stress. It has many effects on the body, including lowering potassium levels, which can cause more symptoms and problems.
According to "Harrison's Principles of Internal Medicine" by Dr. Anthony Fauci, the most common cause of Cushing's syndrome is the administration of cortisol-like drugs, called corticosteroids or just steroids. These drugs are prescribed for numerous conditions involving inflammation, such as asthma or rheumatoid arthritis. They are usually not taken chronically in high doses due to the risk of developing Cushing's. Tumors in the pituitary, a gland below the brain, or in the adrenal glands above the kidneys can also cause the disease, as can some tumors elsewhere in the body that make hormones stimulating the adrenal glands. Some hereditary conditions also can cause the disorder.
The hormone aldosterone is also produced by the adrenal glands. One effect it has is to lower the level of potassium in the body by binding to receptors in the kidney. Cortisol has similar structure to aldosterone and also binds to these kidney receptors, though not as strongly. The result is that cortisol also causes the kidneys to get rid of potassium through the urine, though to a lesser degree than aldosterone. This leads to lower potassium in the blood.
Symptoms and Signs
Cushing's disease produces multiple symptoms and signs. If it causes the potassium to get too low, this will also produce further problems. According to "William's Textbook of Endocrinology" by Dr. Henry M. Kronenberg, common signs of Cushing's include redistribution of fat such that the abdomen, upper body, face and neck tend to be fat relative to the arms and legs. The skin will be fragile and bruise easily. Fatigue, weakness, high blood sugar and blood pressure, mood swings and increased thirst are also common. In addition, sexual desire and fertility may be adversely affected. Low potassium may be without symptoms but can cause weakness and abnormal heart rhythms.
Cortisol can be tested for in the urine, blood and saliva. Usually, urine cortisol is tested by collecting 24 hours of worth of urine. Blood and saliva are typically tested late at night because that is when the cortisol levels are naturally lowest but will be elevated in people with the disease. Another approach is too give a powerful drug that normally suppresses cortisol production, called dexamethasone, to monitor if the levels of cortisol stay elevated, indicating Cushing's. The diagnosis of low potassium is made by a blood test.
Treatment of Cushing's syndrome depends on the cause. Tumors will need to be removed. Inoperable tumors may require radiation or chemotherapy. Low potassium caused by Cushing's disease is ultimately treated by correcting the Cushing's. While the potassium is low, however, oral or IV potassium can be given.
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci et al; 17th Ed.; 2008
- "Williams Textbook of Endocrinology"; Henry M. Kronenberg et al; 11th Ed.; 2007