Dexamethasone test can detect Cushing’s in people with obesity
But scientists call for more selective screening of patients in new study
A low-dose dexamethasone test, which is commonly used to diagnose Cushing’s syndrome, can effectively detect the rare condition in people with obesity, according to a new study.
However, despite the test’s effectiveness, the proportion of patients who ultimately were diagnosed with Cushing’s was low, at 0.2%.
Given that finding, the researchers suggested that screening all patients with obesity for Cushing’s, regardless of the presence of other conditions, is likely impractical and unnecessary. Instead, the team called for more selective screening of individuals with conditions related to so-called unhealthy obesity.
“While the 1 mg [dexamethasone test] is a practical screening test for [Cushing’s syndrome] with high specificity in obesity, the number of … cases detected remains relatively low,” the researchers wrote. “Therefore, it may be more reasonable and applicable to screen patients with [obesity-related conditions] rather than all individuals with obesity.”
Titled “Cushing’s syndrome screening with the 1-mg dexamethasone suppression test in metabolically healthy and unhealthy obesity phenotypes,” the study was published in the International Journal of Obesity.
Investigating if a dexamethasone test should be done for all with obesity
Cushing’s syndrome is characterized by high levels of the hormone cortisol, which is produced by the adrenal glands, located atop the kidneys. Cushing’s disease, one of the most common forms of the syndrome, is caused by a tumor in the brain’s pituitary gland, which leads to the excessive production of ACTH, a hormone that triggers cortisol production.
Cushing’s can lead to a wide range of symptoms, including obesity, high blood pressure, known as hypertension, and diabetes. However, obesity can be a misleading symptom, as it is common in people with Cushing’s, but also has a high prevalence in the general population.
Therefore, there is a need to clarify if regular screening for Cushing’s should be performed in people with obesity.
To determine the prevalence of Cushing’s in people with obesity, researchers in Turkey conducted a retrospective analysis of 1,008 obese patients who underwent the dexamethasone screening test.
The participants had a mean age of 40 and were mostly women (82.8%).
More than three-quarters (77.3%) were also considered to have metabolic unhealthy obesity, meaning they had obesity-related diseases, with almost a quarter having diabetes and 28.9% having prediabetes. These patients had high blood sugar levels, but not high enough to be considered as having diabetes.
Also, 78.4% of these patients had dyslipidemia, or an abnormal level of fatty molecules circulating in the bloodstream. About a quarter (24.8%) had hypertension and 4.2% had coronary artery disease — narrowing or blockage of the arteries that supply blood to the heart.
Compared with patients with metabolic healthy obesity, that is, those who were free from obesity-related conditions, those with unhealthy obesity were significantly older, had a higher body mass index (a measure of body fat), and higher blood sugar levels.
Unhealthy obese patients also had higher levels of triglycerides, a type of fatty molecule, and LDL cholesterol, commonly referred to as bad cholesterol. Conversely, these patients had lower levels of HDL cholesterol, the so-called good cholesterol.
Most found to have Cushing’s were part of unhealthy obese group
The patients were given the dexamethasone test, in which an individual is administered the corticosteroid, which normally blocks cortisol production; in people with Cushing’s, however, cortisol levels do not drop in response to dexamethasone.
After the dexamethasone test, patients with metabolic unhealthy obesity also had significantly higher mean levels of cortisol (0.59 vs. 0.54 micrograms per deciliter, or mcg/dL), the data showed.
Overall, 12 patients (1.2%) had cortisol levels equal to or higher than 1.8 mcg/dL after the test, indicating the presence of Cushing’s. All but one of them were part of the unhealthy obese group, and they commonly had dyslipidemia, abnormal blood sugar levels, and hypertension.
Cushing’s syndrome was eventually confirmed in two of these patients, bringing the overall prevalence of Cushing’s in the entire group to 0.2%. Based on imaging tests, one of the patients was diagnosed with ectopic Cushing’s caused by a lesion in one of the adrenal glands, while the other had Cushing’s disease.
The other 10 patients were considered to have subclinical Cushing’s, meaning their cortisol levels were abnormally high, but they showed no overt signs or symptoms of Cushing’s.
It may be more reasonable and applicable to selectively screen the patients with obesity having comorbidities such as [diabetes], hypertension, dyslipidemia, or coronary artery disease, … rather than all individuals with obesity.
Overall, the low-dose dexamethasone test had a specificity of 99% and a sensitivity of 100% when screening for Cushing’s in people with obesity. Sensitivity refers to the test’s ability to correctly identify patients with the disease, while specificity refers to its ability to correctly identify people without the disease.
However, considering the low prevalence of Cushing’s in the group, researchers argued that “screening all patients with obesity for [Cushing’s syndrome] without considering any associated metabolic conditions appears impractical and unnecessary in everyday clinical practice.”
“It may be more reasonable and applicable to selectively screen the patients with obesity having comorbidities [coexisting conditions] such as [diabetes], hypertension, dyslipidemia, or coronary artery disease, … rather than all individuals with obesity.”
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