This study represents a pioneering investigation into pulmonary involvement in newly diagnosed RA and PsA patients, with a one-year follow-up after treatment initiation. Adopting a comprehensive longitudinal approach, it aimed to assess the utility of various diagnostic modalities in monitoring pulmonary changes and to identify potential biomarkers indicative of pulmonary disease progression.

At baseline, our findings indicated a 37.0% incidence of radiographic pulmonary involvement in patients newly diagnosed with RA and PSA, as previously reported [13]. Specifically, 50.0% o RA patients and 22.7% o PsA patients demonstrated radiographic evidence of pulmonary involvement. Prior prospective studies on pulmonary complications in arthritis predominantly focused on RA, showing a wide range of prevalence rates [6, 20, 39, 40]. For instance, while some studies reported as low as a 10.0% prevalence of pumonary involvement in RA [40], others, like the study by Bilgici et al. employing high-resolution computed tomography and pulmonary function tests, noted abnormalities in up to 67.3% of RA cases [6]. While te baseline findings of our study on RA align with prior research, we observed a significantly higher prevalence of pulmonary involvement in PsA patients than the previously reported 0.5 to 9.4% [29,30,31,32]. The detected revalenc rates at diagnosis for RA and PsA highlight the urgent need for increased awareness, proactive screening, and regular follow-up even in early-stage patients. Moreover, the fact that most patients with pulmonary involvement were asymptomatic necessitates a reevaluation of existing screening protocols to prevent delayed diagnosis and treatment, which could negatively impact patient outcomes. Our study indicates that clinicians should be alert to indicators like high disease activity as measured by DAS28CRP, increased age, and elevated rheumatoid factor levels, even in the absence of symptoms like dyspnea and cough [13].

However, further research is needed to understand not only the initial pulmonary involvement but also its long-term progression and the impact of treatment initiation. Previous studies have mainly utilized imaging techniques to monitor pulmonary progression in RA and PsA, but these methods are limited due to radiation exposure concerns. Our research expands on this by incorporating PFT as an alternative, radiation-free diagnostic method to track longitudinal changes in pulmonary disease progression and to assess the potential reversibility of pulmonary involvement with therapy initiation. Few studies have used PFT in RA [6, 21, 39, 41,42,43,44], and these have highlighted a significant risk for RA patients, especially those with newly diagnosed disease (≤ 2 years), who face a tenfold increased risk of rapid lung function decline, as indicated by a decrease in FVC [39]. Both reduced FVC and high disease activity are independently associated with increased mortality [45]. The utility of PFT in assessing pulmonary involvement in PsA, however, has not yet been explored, rendering our research a pioneering effort.

The absence of a significant association between PFT results, including the 6MWT, and CXR findings at baseline underscores the complexity of pulmonary involvement in RA and PsA. It suggests that early radiographic and functional changes in the lungs may not immediately translate into measurable changes in PFT outcomes. This observation is consistent with the fact that while bodyplethysmography is a suitable and widely available tool for assessing the clinical relevance of lung involvement, it lacks sensitivity, particularly for early and subclinical lesions [41]. Prior studies have not found a significant link between various PFT parameters and lung involvement as detected by high-resolution computed tomography in RA patients [6, 43, 44]. Our findings align with these studies, indicating that while PFT is valuable for evaluating overall lung function and identifying more advanced lung disease, it may not be as effective in detecting early-stage or mild pulmonary involvement. Therefore, it is plausible that some cases of lung involvement may go undetected when relying solely on PFT results, potentially leading to an underestimation of prevalence rates.

During the follow-up period of our study, most functional assessment outcomes, including clinical and laboratory assessments, remained stable. There were no significant changes over time in mean values for FVC, TLC, Tiffeneau index, RV, and DLCO. Additionally, no notable changes were observed in obstructive ventilation disorders. However, the decline in the incidence of restrictive lung disease during the follow-up is noteworthy, despite the lack of an association between arthritis disease activity and the risk of developing restrictive lung disorders. This observation, as well as our baseline results, shows no association between the level of disease activity (as indicated by CRP levels and DAS28CRP score) and the outcomes of PFT, DLCO, or 6MWT, questions an association between disease activity and pulmonary involvement. Our findings suggest that reducing arthritic disease activity does not necessarily reduce the risk or severity of pulmonary involvement.

The existing literature on the relationship between disease activity and pulmonary involvement presents mixed findings. Some studies have found a significant connection between radiographic lung involvement (diagnosed by high-resolution computed tomography) and disease activity (measured by DAS28CRP) [6, 43, 46], and have also linked PFT results to disease activity [42]. In contrast, other research, including a large prospective cohort study, did not find a correlation between DAS28CRP and the risk of pulmonary involvement diagnosed by high-resolution computed tomography, nor between PFT results and DAS28CRP [20, 39]. In our study, smoking, BMI, and symptom duration showed no significant associations with pulmonary function across study visits. These findings partially contradict existing literature, which identifies smoking history and arthritis symptom duration exceeding five months as risk factors for interstitial lung disease in rheumatoid arthritis [47]. The lack of significant associations in our study may be attributable to the relatively small sample size. Moreover, pulmonary changes in arthritis patients may develop over extended periods, highlighting the need for longer follow-up or more sensitive pulmonary assessments to capture these effects. This underscores the complexity of pulmonary involvement in arthritis and the necessity for further research to better understand its multifactorial etiology.

The improvement in walking distance, as measured by the 6MWT, independent of disease activity, further suggests multifactorial influences on functional capacity. The outcomes of the 6MWT might be affected by a combination of factors beyond disease activity. These factors could include a reduction in arthritis-associated pain, leading to increased daily activity and mobility, which in turn might result in training effects improving overall functional capacity. Additionally, improvements in pulmonary capacities behavioral adaptations may contribute to the enhanced walking distances observed. Conversely, arthritis-associated pain, particularly when involving weight-bearing joints such as the knees, and limited mobility may adversely impact 6MWT performance. Our findings highlight that, while the 6MWT is a valuable tool for assessing functional capacity, its results in arthritis patients should be interpreted within the context of diverse influencing factors. These factors extend beyond disease activity and pulmonary involvement, emphasizing the complexity of functional assessments in this patient population.

Furthermore, our study found no significant association between rheumatological medications and PFT or 6MWT results, suggesting that early-stage medication choices may not have a substantial impact on lung function or capacity. Notably, our study did not detect evidence of potential drug-induced lung diseases within the observed timeframe. This absence of evidence offers some reassurance about the short-term pulmonary safety of these medications, but it is crucial to maintain vigilance for possible long-term pulmonary effects [48].

In summary, our study underscores the frequent occurrence of pulmonary involvement in newly diagnosed, untreated RA and PsA patients, many of whom display no symptoms. The considerable impact of pulmonary involvement on the quality of life, morbidity, and mortality in these patient groups emphasizes the need for thorough monitoring, particularly during the early years of disease activity and upon therapy modification. Although CXR, PFT with DLCO, and 6MWT emerge as potential diagnostic tools for initial assessment and tracking, our study revealed no significant changes over time, indicating the need for more sensitive and specific diagnostic tools.

While our research provides important insights into the pulmonary involvement of RA and PsA, it also highlights the need for further research with several limitations warranting consideration. Larger-scale studies with extended follow-up periods are essential to validate our findings and better understand the long-term evolution of pulmonary involvement and its responsiveness to therapy. Moreover, the relatively small sample size reduces the statistical power to detect subtle subgroup differences and limits the generalizability of our findings. Additionally, the diagnostic methods used also have inherent limitations. While chest radiography and pulmonary function tests are practical and widely accessible, they may lack the sensitivity needed to detect early or subtle pulmonary abnormalities. Advanced imaging techniques, such as HRCT, could offer more precise insights into the extent and nature of pulmonary changes.

Future studies could benefit from a more comprehensive assessment of disease manifestations, particularly when evaluating axial and peripheral disease involvement. The DAS28-CRP, while a valuable tool for assessing peripheral joint disease activity, may not adequately capture axial PsA manifestations, thereby limiting the understanding of their relationship with pulmonary involvement. Additionally, this study did not separately evaluate arthritis localization or the number of affected joints, both of which could provide critical insights into their potential impact on pulmonary function. Finally, the comparative approach in this study, analyzing RA and PsA side by side, offers important insights but also presents challenges. These diseases have distinct pathophysiological mechanisms, which may reduce the applicability of unified conclusions. Addressing these differences in future studies by tailoring methodologies to the unique features of each condition will improve the understanding of their respective pulmonary complications.