Ratio of fat and muscle in hips may aid Cushing’s detection

IVR correctly ID'd all the Cushing’s patients, 80% without it, in one group

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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A doctor reviews images on an MRI chart.

A CT scan-based measurement of the amount of fat and muscle tissue around the hips may help identify Cushing’s syndrome in older female patients with adrenal tumors.

That’s according to the study, “Iliopsoas muscle to visceral fat ratio on CT predicts Cushing’s syndrome in elderly females with adrenal tumors,” which was published in the Endocrine Journal

Cushing’s syndrome is a broad term encompassing diseases whose symptoms are driven by elevated levels of the stress hormone cortisol. Cushing’s disease is a specific form of it that’s caused by a tumor in the brain’s pituitary gland. Cushing’s syndrome can also be caused by tumors in the adrenal glands, located above the kidneys, which are mainly responsible for making cortisol.

Masses can develop on the adrenal glands without causing any notable issues. In fact, adrenal masses are incidentally found in up to 5% of CT scans of the abdomen, particularly in elderly patients. This can be a challenge for clinicians to know if an incidentally discovered adrenal growth is actively contributing to a patient’s health problems.

The researchers proposed measuring the amount of visceral fat and muscle tissue to help identify adrenal growths most likely to cause Cushing’s. Visceral fat, sometimes called “hidden” fat, is stored deep inside the body, between internal organs. Subcutaneous fat, the other main type of fat, sits just below the skin.

Prior studies using CT scans have suggested visceral fat is higher with Cushing’s syndrome, while muscle mass tends to decrease.

Researchers measured the amount of visceral fat in the lower pelvis, specifically at the level of the third lumbar vertebrae. They also measured the area of the iliopsoas muscle, one of the main muscles of the hips, and calculated the ratio of muscle area to visceral fat, referred to as IVR.

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Measuring visceral fat to ID Cushing’s syndrome

These measures were assessed in 24 women with adrenal tumors, ages 56-77. Nine had Cushing’s syndrome, while the other 15 had tumors that weren’t causing notable health problems.

The median total visceral fat area was significantly higher among Cushing’s patients. The median iliopsoas muscle area was significantly lower. The median subcutaneous fat area didn’t differ significantly between those with or without Cushing’s. The median IVR was significantly lower in patients with Cushing’s (0.04 vs. 0.1).

To assess IVR’s ability to identify patients with Cushing’s, researchers used a statistical analysis called the area under the curve (AUC), which tests how well a given measure can distinguish between two groups —  in this case, those with and without Cushing’s. AUC values can range from 0.5 to 1, with higher numbers reflecting a better ability to differentiate.

With a cutoff value of 0.067, the AUC for IVR was 0.933, with the ratio correctly identifying all the Cushing’s patients and 80% of those without it.

“This study showed that a novel numerical index, the IVR, was useful for predicting [Cushing’s syndrome] in elderly female patients with adrenal tumors,” the researchers wrote.

The analyses were repeated in a separate group of elderly female patients with adrenal tumors — seven with Cushing’s and 16 without. Using the same cutoff value of 0.067, the IVR correctly identified 71.4% of the Cushing’s patients and 87.5% of those without it.

Among six Cushing’s patients from both groups with available data, IVR tended to increase after treatment.

The researchers emphasized that their analysis was limited by the small number of patients, but noted the findings support using IVR as a measure to identify Cushing’s among elderly women with adrenal tumors. More research is needed to validate the findings, they said, adding establishing how IVR values normally vary based on factors like age may make the measure more useful.