People with Cushing’s syndrome experience muscle weakness that persists even when the disorder is in remission, a new study shows.
Cushing’s syndrome is characterized by abnormally high levels of the hormone cortisol. This can result in a variety of symptoms, including muscle weakness. However, it’s unclear the extent to which treatment of the underlying syndrome affects muscle weakness in the long term.
In the new study, researchers analyzed data for 88 people with endogenous Cushing’s syndrome diagnosed between 2012 and 2018 who had undergone regular muscle function tests. The data were collected as part of the German Cushing’s Registry, and the assessed group was mostly female (78%), with an average age of 49.
Of note, not all individuals had data available for every time point assessed — for example, at four years of follow-up, data were available for only 22 of the people analyzed.
Of the 88 individuals assessed, 49 had Cushing’s disease (a form of Cushing’s syndrome driven by a tumor on the pituitary gland). All 88 underwent curative surgery. The median time between diagnosis and remission was two months.
The researchers measured muscle strength in two ways: by grip strength and the chair rising test.
On average, and after statistical adjustments for age and sex, grip strength at diagnosis was 83% (with 100% reflecting the average for people without Cushing’s syndrome). Six months after surgery, average grip strength had decreased to 71%. A year after surgery, average grip strength was 77%. At all time points measured, up to four years after surgery, grip strength was significantly lowered in people with Cushing’s syndrome.
The chair rising test (CRT) involves measuring how quickly a person can rise from a seated position. Generally, being able to do so more quickly indicates greater muscle strength. People with Cushing’s syndrome showed improvement in the CRT six months after treatment (median 7 seconds), compared to the beginning of the study (8 seconds).
However, no further improvement was observed at subsequent time points up to four years, and compared to controls, CRT remained abnormal over time (7 seconds in Cushing patients at three years of follow-up vs 5 seconds in controls).
“The main finding of our study is that muscle strength remains impaired even after years in remission,” the researchers wrote.
“Another interesting finding is that at 6 months follow-up grip strength and CRT performance show opposite effects. Whereas grip strength has worsened, CRT performance has improved,” they added.
The investigators speculated that this difference is probably due to changes in body weight. Cushing’s syndrome commonly results in weight gain, and treatment resulted in significant decreases in body mass index in the analyzed group. As such, it may have been easier for individuals to stand up because there was less mass for their muscles to move, not necessarily because their muscles were stronger.
“Why patients with CS in remission showed a temporary worsening in grip strength 6 months after surgery remains unclear in terms of pathophysiology,” the researchers wrote.
They speculated that this could be due to treatment with glucocorticoids, which may affect muscle strength, but added that, “Whether the necessity of a long-term glucocorticoid replacement influences muscle strength or myopathy [muscle disease] outcome remains controversial.”
The researchers also conducted statistical analyses to determine what patient factors were associated with poorer muscle function outcomes. They found statistically significant associations between poor muscle function and older age, higher waist-to-hip-ratio, and higher levels of HbA1c (a marker of metabolic disease like diabetes).
“Influencing factors for myopathy outcome are age, waist-to-hip-ratio and HbA1c, suggesting that a consistent and strict treatment of diabetic metabolic state during hypercortisolism [high cortisol levels] is mandatory,” the investigators wrote.
The study was limited by its small sample size, the researchers noted, particularly at longer follow-up times, and by the fact that only a few measurements of muscle strength were used. Additionally, since all the data were collected at one of three centers in Germany, the analyzed population may not be representative of the worldwide population of people with Cushing’s syndrome.
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