Lower baseline diffusing capacity of the lungs for carbon monoxide by single breath was associated with a higher likelihood of progression to systemic sclerosis and a shorter time to transition in patients with very early disease, according to a retrospective longitudinal study.
In the cohort of 73 patients, 12% progressed to definite systemic sclerosis (SSc) over a median follow-up of 5 years. Patients with baseline carbon monoxide by single breath (DLCO/SB) below 70% had higher progression rates than those with values of 70% or higher (33% vs 8%) and progressed sooner, with an estimated time to transition of 7.7 years versus 10.2 years.
All patients who progressed were positive for SSc-specific antibodies and had lower baseline DLCO/SB than patients who remained stable (68% vs 81%). Lung volumes, including forced vital capacity and total lung capacity, were similar between groups at baseline, indicating preserved lung volumes despite reduced gas transfer in patients who later progressed.
In adjusted analyses, SSc-specific antibodies and scleroderma-pattern nailfold videocapillaroscopy findings appeared to contribute most to progression risk, whereas reduced DLCO/SB had a more limited independent association. The researchers noted that no variable reached statistical significance in the multivariable model.
Among patients who did not transition to definite SSc, pulmonary function declined over time. In the subgroup with follow-up testing, a decrease in DLCO/SB of at least 15% occurred in 24% of antibody-positive patients compared with 6% of antibody-negative patients, with earlier decline in the antibody-positive group (8 years vs 10.4 years).
Declines in forced vital capacity of at least 10% were frequent overall and numerically more common in antibody-positive patients (88% vs 64%), though differences in time to decline were not statistically significant. Nailfold videocapillaroscopy pattern and puffy fingers were not associated with significant differences in time to pulmonary function decline.
The researchers wrote that baseline DLCO/SB below 70% “is a potential marker of disease progression” in very early SSc and noted that subtle pulmonary function decline may occur even in patients who do not meet classification criteria for definite disease. However, they did not establish DLCO/SB as an independent predictor of progression.
The study evaluated patients undergoing annual pulmonary function testing at a single center, with progression defined by 2013 American College of Rheumatology/European Alliance of Associations for Rheumatology criteria.
Limitations included the retrospective single-center design. In addition, not all patients underwent high-resolution computed tomography; in some cases, absence of interstitial lung disease was inferred from chest x-ray findings combined with clinical data, which may have limited detection of subclinical disease.
Disclosures: Author disclosures were available with the study.
Source: American College of Rheumatology / ACR Open Rheumatology
