Reply: Quantitative Computed Tomography in Systemic Sclerosis–Interstitial Lung Disease: Are We Ready to Go beyond Standard Assessment?

From the Authors:

We thank Dr. Ariani for his comments on our recent publication that describes the limitations of simple quantitative computed tomographic (CT) measures in systemic sclerosis (SSc)–associated interstitial lung disease (ILD) (1).

We agree that excluding patients with significant emphysema could have improved the prognosis of our study cohort; however, only 1.0% of the scans available for our cohort met the exclusion criterion of having emphysema affecting >10% of total lung volume. Exclusion of this small group of patients is unlikely to have significantly impacted the prognosis of our cohort and is similarly unlikely to have biased our main finding showing a lack of independent association between density-based quantitative CT measures and survival.

We similarly recognize the potential of user-friendly independent operator algorithms that are based on open-source digital imaging and communications in medicine–viewer software (e.g., OsiriX and Horos). However, the utility of currently available imaging software remains limited by widely varying CT protocols. Consequently, we were only able to quantitively analyze 38% of all available CT scans, with the majority of scans excluded on the basis of being nonvolumetric (45%), having contrast (24%), or being taken in the prone position (12%).

ILD protocols are now making more use of the volumetric CT protocols available with modern multidetector CT scans, and we believe that some of these limitations can be overcome. However, our results suggest that simple density-based quantitative CT measures do not add prognostic value to readily available pulmonary function variables in patients with SSc-ILD. This indicates that further work is needed not only to overcome the above challenges but also to demonstrate true clinical utility of more complex quantitative CT measures. We look forward to taking these next steps together with Dr. Ariani and many others who are actively working in this important and rapidly evolving area.