Shear-wave Elastography May Best Capture Changes in Skin Stiffness

A form of ultrasound imaging called shear-wave elastography (SWE) is more sensitive for assessing changes in skin stiffness over time in scleroderma (SSc) patients than the current gold standard measure, a study suggested.

Because a lessening in skin stiffness was also observed in healthy people, skin changes seen in scleroderma patients may be partly explained by normal aging, its researchers said.

The study, “How much of skin improvement over time in systemic sclerosis is due to normal ageing? A prospective study with shear-wave elastography,” was published in Arthritis Research and Therapy.

Measuring skin involvement is essential for diagnosing scleroderma, and for assessing likely outcomes and disease progression. The extent of  skin fibrosis, or scarring, is also known to correlate with internal organ involvement.

The gold standard measure of skin changes in SSc is the modified Rodnan skin score (mRSS), a method based on palpation and calculated by adding scores of skin thickness taken at 17 different sites. This assessment is also often used to determine efficacy in clinical trials of potential scleroderma therapies.

However, the Rodnan score has been criticized for limitations that include a lack of objectivity and of sensitivity to skin thickness over time.

SWE, which works by measuring the velocity of shear waves, has been investigated as an alternative way of determining skin stiffness. The faster the waves propagate, the stiffer the tissue.

“SWE may, therefore, provide a novel opportunity to objectively assess fibrosis — a crucial feature in the complex process of skin involvement in SSc,” the researchers wrote.

Previous studies showed that SWE values are significantly higher in scleroderma patients than in controls, in almost all sites on the body assessed using the modified Rodnan score. Scientists also found that skin still unaffected by palpable standards could be better distinguished from the skin of healthy people using SWE.

To evaluate skin stiffness progression using SWE in people with and without scleroderma, researchers at University of Coimbra, in Portugal, evaluated 21 patients (85.7% females, mean age 56.3) and 15 healthy people (control group). Among the patients, 57.1% had limited scleroderma.

Skin stiffness, measured by shear-wave velocity in meters per second, was assessed at 17 sites at the study’s start and again over almost five years of follow-up (median of 4.9 years). Measures at these sites using the modified Rodnan scale were also taken.

Results showed that, at follow-up, shear-wave velocity values in scleroderma patients were significantly lower at all skin points, except in the fingers. Modified Rodnan scores only detected significant changes in patients’ upper arms and forearms.

“Shear-wave elastography was remarkably more sensitive to change over time than mRSS,” the researchers wrote.

Among healthy controls, shear-wave velocity values also decreased over time, although to a lesser degree, at all sites except the legs.

The percentage change in shear-wave velocity from the study’s start was variable across skin sites, and more pronounced in the scleroderma group, particularly in the upper arm and chest.

“This is in line with studies that have identified the chest and forearms as the sites with more pronounced skin changes over time, as opposed to the lower extremities, abdomen, fingers, and face, which tend to be more stable,” the researchers wrote. “These findings raise the hypothesis that excluding relatively static skin sites may improve the sensitivity to change of total skin scores.”

Scientists also observed that shear-wave velocity values were in accordance with disease stage. At the study’s start, five patients in the early edematous phase (with swelling) had higher values than patients in a fibrotic phase. These values decreased over follow-up, corresponding to the greater drop in velocity values in patients in the earlier phase, the onset of fibrosis, and progression to atrophy (shrinkage).

“This may be particularly important in the assessment of the early phases of disease and response to treatment,” the investigators wrote.

“Surprisingly, however, our observations in healthy controls suggest that a substantial part of the decrease in skin stiffness observed in patients with SSc is probably explained by normal skin ageing,” they added.

Specifically, the researchers calculated that aging seemed to explain from 40% (leg) to 90% (chest) of the skin stiffness reduction seen in scleroderma patients.

Notably, most (72.2%) of these people were older than 50 at the study’s start. Other factors such as gender, hormonal changes and skin site, may also explain the results, the scientists said. About half of the patients were also taking immunosuppressive treatments during the study period, which may have influenced results.

Overall, “a relevant key message from our findings provides the evidence that skin SWV [shear-wave velocity] evaluation is a more sensitive instrument to measure skin change over time than mRSS,” the investigators wrote.

Because SWE and Rodnan measure different skin properties, future studies are needed to validate SWE against changes at the tissue level (histology) as well.

These findings “support the higher discriminant ability of [SWE] in detecting subtle skin changes not identified by mRSS,” the researchers wrote.

“Further longitudinal studies with a higher number of patients in different phases of skin involvement are needed to fully clarify its potential. Establishing normal reference data for these ultrasound measurements may also foster earlier diagnosis,” they concluded.