Though the body produces many hormones, the role of cortisol is especially important. Cortisol is a stress hormone that affects the heart, cardiovascular system, blood pressure, water excretion and electrolyte balance. Cortisol is also responsible for mobilizing fatty acids from adipose tissue and acting as an anti-inflammatory, and it is the hormone primarily responsible for directing peak performance of the immune system. When the body is under stress, it almost immediately begins to increase levels of cortisol in an effort to prepare to defend itself against whatever is causing the stress. In its absence, or when cortisol levels are insufficient, the result is depressed immunity from virtually every pathogen.
Causes of Cortisol Deficiency
Cortisol deficiency, also known as adrenal insufficiency, can be either a primary or secondary insufficiency. The degree of insufficiency depends upon whether adrenocorticotropic hormone (ACTH) is stimulating the adrenal glands enough, or at all. Without ACTH, cortisol production will be low. Inadequate secretion of ACTH by the pituitary gland is the most common cause of secondary adrenal insufficiency. In this case, cortisol is present but not being secreted, or secretion is inadequate. Primary adrenal insufficiency, on the other hand, is caused by a disorder of the adrenal glands themselves. In this case, cortisol is missing completely. To determine the degree to which cortisol is deficient, various tests may be administered.
Symptoms
Symptoms of cortisol deficiency commonly include chronic fatigue that becomes progressively worse, muscle weakness, loss of appetite, low blood pressure, irritability, depression, hypoglycemia (low blood sugar), irregular menstrual periods and weight loss. Roughly 50 percent of patients will also experience nausea, vomiting and diarrhea. Often, symptoms slowly progress and go unnoticed until there is an acute adrenal crisis. Symptoms of an acute adrenal crisis (addisonian crisis) include sudden pain in the lower back, abdomen or legs, severe vomiting and diarrhea, dehydration, low blood pressure and loss of consciousness. Left untreated, an acute adrenal crisis can be fatal.
ACTH Stimulation Testing
The ACTH stimulation test is the most specific test available for accurately diagnosing adrenal hormone levels. Blood cortisol, urine cortisol or sometimes both are analyzed before and after synthetic ACTH is administered via injection. After ACTH is delivered intravenously, cortisol in the blood is measured every 30 to 60 minutes. If there is a rise in both blood and urine cortisol levels, the response is considered "normal." Adrenal insufficiency is suspected if patients respond poorly or don't respond at all.
CRH Stimulation testing
If the patient's response to the short ACTH test is abnormal, then a "long" stimulation test is performed. The long test, also called a CRH stimulation test, helps determine the cause of the insufficiency. Synthetic CRH is again injected intravenously, then blood cortisol levels are measured before as well as at 30, 60, 90 and 120 minutes following injection. If the cause of adrenal insufficiency is the pituitary gland, patients will typically have no ACTH response at all. If the cause is the hypothalamus, the ACTH response will usually be delayed. A high ACTH response, but with no cortisol production, is the hallmark of Addison's disease, also known as primary adrenal insufficiency.
Imaging Tests
If adrenal insufficiency is diagnosed, additional imaging tests may be required to see if there are signs of calcium deposits on the adrenal glands, which can indicate tuberculosis. If calcium deposits are discovered, a TB skin test may be administered. If the cause of adrenal insufficiency is secondary to another cause, imaging tools, such as an MRI or CT, may be used to look at the pituitary gland for possible abnormalities, injury or the presence of a pituitary tumor.
