Cardiopulmonary exercise testing complements both spirometry and nuclear imaging for assessing sarcoidosis stage and for monitoring disease activity

Background: Pulmonary sarcoidosis is a systemic disease that can confound established follow-up tools. Pulmonary function tests (PFTs) are recommended in initial and follow-up patient evaluations yet are imperfect predictors of disease progression. The cardiopulmonary exercise test (CPET) is another potentially useful monitoring tool, although previous studies report conflicting findings regarding which variables are altered by the disease. Nuclear imaging tests are also employed to assess inflammatory activity and may be predictive of functional deterioration. Aim: We asked whether PFTs or CPET are more diagnostic of disease stage, which subsets of functional variables are impacted by the disease, and how these relate to nuclear imaging signs of active inflammation. Study design and methods: We collected retrospective data (spirometry, CPET, Gallium-67 scintigraphy, 18F-FDG PET/CT) from 48 patients and 10 controls. Disease severity was assessed following Scadding classification. First, we correlated individual PFTs and CPET parameters to Scadding stage and nuclear imaging data. Next, we performed Principal Component Analysis (PCA) on PFTs and CPET parameters, separated into respiratory, cardiovascular and metabolic subsets. Finally, we constructed multiple regression models to determine which variable subsets were the best predictors of Scadding stage and disease activity. Results: The majority of PFTs and CPET single parameters were significantly correlated with patient stage, while only few correlated with disease activity. Nevertheless, multiple regression models were able to significantly relate PFTs and CPET to both disease stage and activity. Additionally, these analyses highlighted CPET cardiovascular parameters as the best overall predictors of disease stage and activity. Conclusions: Our results display how CPET and spirometry data complement each other for sarcoidosis disease staging, and how these tests are able to detect disease activity. Our findings suggest that CPET, a repeatable and non-invasive functional test, should be more routinely performed and taken into account in sarcoidosis patient follow-up.