Novel Imaging Method for Skin Disease Passes Early Scleroderma Test

— Noninvasive and nonradiological, this new technology may outperform Rodnan scoring

An emerging technique called spatial frequency domain imaging (SFDI) proved its mettle for evaluating skin fibrosis in systemic sclerosis (SSc), also called scleroderma, in an early clinical study.

Comparing SFDI parameters with modified Rodnan Skin Score (mRSS) values and findings from histological biopsy analyses yielded correlations strong enough that the new approach deserves additional testing in larger samples, according to Andreea M. Bujor, MD, PhD, of Boston University (BU), and colleagues writing in Lancet Rheumatologyopens in a new tab or window.

Moreover, because SFDI is a noninvasive imaging modality based on ordinary visible light, the researchers were able to perform frequent serial tests over a 4-year period -- far more often than is practical for objective evaluations that depend on biopsies. Those results, too, supported SFDI for routine monitoring in SSc and potentially other skin diseases.

"Changes in SFDI parameters correlated with changes in mRSS, suggesting that SFDI can track within-patient change over time," the authors wrote. "However, because the longitudinal sample was modest and change-score analyses can be influenced by regression to the mean, these findings should be interpreted cautiously and confirmed in larger prospective cohorts."

Because fibrosis and other skin pathologies in SSc go deep into the organ's many layers, it's not enough for clinicians to simply eyeball patients' skin; physical exam, in which the clinician pinches the patient's skin at various locations, is the basis for mRSS scoring. More objective assessment means biopsies and microscopic inspection. The latter must therefore be performed infrequently, such that important but subtle changes are likely to be missed for months or even years.

SFDI was introduced in 2009opens in a new tab or window for "quantitative, wide-field characterization of optical absorption and scattering properties of turbid media." The Journal of Biomedical Optics, where this initial paper appeared, has since featured numerous studies by different groupsopens in a new tab or window (mostly in Asia) seeking to develop it for skin disease applications.

Bujor's team has been among themopens in a new tab or window with a particular interest in SSc. For this latest studyopens in a new tab or window, the investigators recruited a total of 54 SSc patients and 30 healthy controls who were to come into the BU clinic for ultrasound, durometry, and SFDI scans. The study was divided into a pilot phase, with 10 patients and eight controls who came for a single visit including the various scans and optional forearm biopsies, and then an expanded phase with additional enrollees along with some holdovers from the pilot. In this second part, participants came every 3 months for the first year and every 6 months for another 3 years. Scans were performed and Rodnan scores calculated at these visits. In total, 49 patients and 25 controls provided data adequate for the final analysis (one patient lacked SFDI results but did provide the optional biopsy and so was included).

Three-quarters of SSc patients had the diffuse cutaneous form and all but one of the rest had limited skin involvement. Disease duration varied considerably, with 41% showing symptoms for less than 2 years and 31% with duration beyond 5 years. Rodnan scores averaged 11 (SD 9) at baseline.

Two SFDI parameters were tracked: diffuse reflectance (R_d) and the reduced scattering coefficient (μ_s′). These correlated reasonably well with mRSS values, with a range of -0.38 to -0.48 in the r coefficient. Correlations were similar between SFDI and histological findings of fibrosis (r -0.34 to -0.52). Values for both R_d and μ_s′ were significantly lower in patients versus controls irrespective of Rodnan score, the authors reported.

They emphasized that SFDI is nowhere near ready for widespread clinical use. "Future work should prioritize handheld device optimization, validation in larger and more diverse longitudinal cohorts," they wrote, "spanning very early to long-standing disease, establishment of thresholds of meaning for change, and integration of patient-reported outcomes to link optical changes with patient-perceived improvement."

As well, the current study came with numerous limitations. Bujor and colleagues noted that the patient sample was small and not fully representative of the general SSc population. Also, many potential confounders such as patients' medications, sun exposure, and smoking status were not accounted for.