Cushing's Syndrome & Disease - Diagnosis

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How is Cushing’s Syndrome Diagnosed?

Because not all people with Cushing’s syndrome have all signs and symptoms, and because many of the features of Cushing’s syndrome, such as weight gain and high blood pressure, are common in the general population, it can be difficult to make the diagnosis of Cushing’s syndrome based on the symptoms alone. As a result, doctors use laboratory tests to help diagnose Cushing’s syndrome and, if that diagnosis is made, go on to determine whether it is caused by Cushing’s disease or not. These tests determine if too much cortisol is made spontaneously, or if the normal control of hormones isn’t working properly.

Cortisol measurements
The most commonly used tests measure the amount of cortisol in the saliva or urine. It is also possible to check whether there is too much production of cortisol by giving a small tablet called dexamethasone that mimics cortisol. This is called a dexamethasone suppression test. If the body is regulating cortisol correctly, the cortisol levels will decrease, but this will not happen in someone with Cushing’s syndrome.

These tests are not always able to definitively diagnose Cushing’s syndrome because other illnesses or problems can cause excess cortisol or abnormal control of cortisol production. These conditions that mimic Cushing’s syndrome are called ‘pseudo-Cushing’s states’ and include the conditions shown in Table 2. Because of the similarity in symptoms and laboratory test results between Cushing’s syndrome and pseudo-Cushing’s states, doctors may have to do a number of tests and may have to treat conditions that might cause pseudo-Cushing’s states – such as depression – to see if the high cortisol levels become normal during treatment. If they do not, and especially if the physical features get worse, it is more likely that the person has true Cushing’s syndrome.

Table 2: Pseudo-Cushing’s states

Pseudo-Cushing’s states
Strenuous exercise
Sleep apnea
Depression and other psychiatric disorders
Uncontrolled diabetes
Extreme obesity