Several studies demonstrated poor HRQoL in patients with respiratory diseases including sarcoidosis [2, 6, 7, 24–26, 29, 31–36]. Using two commonly employed health related questionnaires we assessed the QoL of patients with sarcoidosis and attempted to identify the physiologic parameters that best predict QoL measures. Through statistical modeling, we determined that the best prediction of QoL scores can be achieved by integration of two simple values obtained from the 6MWT: DSP and BDSS at 6 min. Substitution of DSP value with 6MWD in the very same regression model resulted in a lower R2. Others found a relationship between 6MWD and HRQoL measures . In our data set, oxygen saturation at 6 min did correlate with HRQoL measures in addition to PFT values, especially DLCO (data not shown). The DSP is a calculation derived from 6MWD and the lowest saturation at 6 min and has been shown to predict poor outcome in patients with IPF . We conclude that HRQoL can best be predicted by DSP and the BDSS at 6 min and that these two parameters may be used as surrogates for HRQoL measures as determined by these two commonly used questionnaires. The 6MWT and dyspnea scores have previously been shown to be correlated to improvements in HRQoL scores [18, 32, 37, 38]. A previous report addressed the reproducibility of the 6MWT among patients with fibrotic lung diseases and found that 6MWD is fairly reproducible. Interestingly, although the amplitude of desaturation among those patients varied, survival among those patients best correlated with the amplitude of oxygen desaturation as the strongest predictor of mortality . The results of our study clearly demonstrate a significant relationship between DSP and HRQoL scores as determined by either SF-36 or SHQ and that DSP is a better predictor as compared with 6MWD.
Assessment of dyspnea is an important factor in evaluating the functional status of patients with diverse diseases and it has high impact on HRQoL scores [6, 37, 38]. Our findings concur with previous studies. Since exercise training and pulmonary rehabilitation may increase exercise capacity, reduce dyspnea and increase distance walked, these variables can be targeted for intervention and may impact positively on outcomes and HRQoL [37, 38].
Questionnaires designed to evaluate HRQoL have been validated and have been shown to improve patient-physician communication and counseling regarding aspects of QoL . Previous studies have found that PFT values are not reliable markers to predict HRQoL in patients with COPD [6, 7, 31]. In the current study, FEV1, FVC and DLCO were found to have significant associations with HRQoL scores on univariate analyses, but not in the multiple regression models. No association was found between HRQoL scores and steroid use in our study, in contradiction to earlier studies [33–35]. Patients with obesity have also been shown to have poor HRQoL scores, but no statistically significant association was found between BMI and the HRQoL scores in our study [36, 41].
The SHQ is the only questionnaire specifically designed to assess HRQoL in patients with sarcoidosis. It was originally devised and validated with the SF-36 by Cox et al. . Our study independently validated the SHQ with the SF-36 in a large cohort of patients with sarcoidosis. Additionally, we compared the different domains assessed by both questionnaires and found that the SHQ-PS correlated well with SF-36-PCS, as did the SHQ-ES score with SF-36-MCS. Because of its disease-specific nature, we hypothesized that the SHQ would be a better measure of HRQoL than the SF-36 in sarcoidosis patients. However, this hypothesis was not supported by the evidence reported here. One possibility is that the SHQ is differently weighted in regard to organ involvement as compared with SF-36. SHQ would likely perform better than a respiratory-specific measure of HRQoL, but we did not include this type of questionnaire in our study.
QoL is not only affected by disease severity, but also by the social and occupational limitations imposed by the disease. Ethnicity may impact QoL in conditions like sarcoidosis due to its influence on both disease severity and access to healthcare . One limitation of this study is that the sample consists almost entirely of African American women. Because of minimal variation in ethnicity there may be racial differences not detected from this data set.
This study is also limited by the fact that we could not account for all comorbid conditions, including PH, which may affect patients with sarcoidosis. Among the study patients, 17% had known PH as confirmed by right-sided cardiac catheterization (See Table 1). Recently, we have shown that a decreased oxygen saturation level at completion of 6MWT is highly predictive of the presence PH in patients with sarcoidosis . These patients also tend to have a lower oxygen saturation resulting in a lower DSP. Additionally, we have not assessed fatigue in this study, which has been shown to be an important component of HRQoL and may impact the 6MWD . Overall, the correlation of HRQoL measures and PFT values was lower as compared to correlation of those measures with values derived from 6MWTs. This finding is not entirely surprising. Due to the systemic nature of sarcoidosis, other systemic involvements, besides lung function, such as musculoskeletal involvement or fatigue may have contributed to the decrease in HRQoL measures. Finally, logistically we could not always obtain the PFT, 6MWT and questionnaires on the same day because of operational constraints at our institution. This might be considered a limitation of our study; although, it is unlikely that within weeks PFT values or 6MWTwould have changed to the extent that have influenced the results.
Our study is unique in attempting to identify commonly used clinical parameters as surrogate markers to predict HRQoL in chronic sarcoidosis. The DSP and BDSS at 6 min showed a significant association with HRQoL scores and, therefore, may be used to predict HRQoL in patients with sarcoidosis. These parameters may serve as potential targets for intervention to improve HRQoL. Further study is needed to validate the value of DSP as a universal measure for the assessment of HRQoL in other chronic respiratory diseases that lead to oxygen desaturation during exertion, such as COPD and IPF.