Measurement properties of the Portuguese version of Pulmonary Functional Status and Dyspnea Questionnaire - modified version (PFSDQ-M) and the Canadian Occupational Performance Measure (COPM) in interstitial lung disease

Abstract

Introduction and objectives: There are several instruments to assess functional status, however, their measurement properties for specific populations are often unknown. The aim of this study was to assess the reliability and validity of the Pulmonary Functional Status and Dyspnea Questionnaire - modified version (PFSDQ-M) and the Canadian Occupational Performance Measure (COPM) for Portuguese adults with interstitial lung disease (ILD). Methods: An observational study was conducted with people with ILD. Sociodemographic and clinical data [lung function and 6-minute walk test (6MWT)] were retrieved from participants’ medical notes. At baseline, the PFSDQ-M, the COPM, the St. George’s Respiratory Questionnaire for idiopathic pulmonary fibrosis (SGRQ-I) and the London Chest Activities of Daily Living (LCADL) were first collected face-to-face, in an interview form. PFSDQ-M and COPM were repeated 48h-72h after by two raters, via phone call. Reliability measures included Cronbach’s to test internal consistency, intraclass correlation coefficient (ICC2,1) and respective 95% confidence intervals (95%CI) for test-retest/intra-rater and inter-rater reliability, Bland & Altman 95% limits of agreement (95%LoA), standard error of measurement (SEM) and minimal detectable change (MDC95) for test-retest measurement error. For COPM, two raters classified all activities mentioned by the International Classification of Functioning, Disability and Health (ICF) second level classification. Interrater agreement was assessed through Cohen’s kappa. Validity was assessed with the Spearman correlation coefficient (rho): criterion validity between LCADL and PFSDQ-M and COPM, and construct/ divergent validity between lung function, 6MWT, SGRQI and PFSDQ-M and COPM. Floor and ceiling effects were explored and considered existing If more than 15% of participants were at the maximum or minimum score. Results: 167 people with ILD (64 ± 14 years old; 49% male; FVCpp 87 ± 20; DLCOpp 62 ± 21) participated. PFSDQ-M showed excellent internal consistency (= 0.92 a = 0.97), good test-retest and interrater reliability (ICC2,1 = 0.76-0.87, 95%CI [0.65,0.91] and ICC2,1 = 0.84-0.87, 95%CI [0.75,0.92], respectively), and good agreement between moments (mean = 7.47, LC95% [-46.06, 61.00]) and raters (mean = -0.24; LC95% [-52.63; 52.14]), without evidence of systematic bias. SEM and MDC95 ranged from 0.56-2.38 e 1.56-6.60, respectively. Correlations between PFSDQ-M and: SGRQ-I and LCADL were significant, positive, and moderate to high (= 0.59 to 0.82, p < 0.01; lung function and 6MWT were significant, negative, and small to moderate (= -0.23 a -0.44; p < 0.01). COPM showed good to excellent test-retest/intra-rater and inter-rater (ICC2,1 = 0.78- 0.86, 95%CI [0.66,0.91] and ICC2,1 = 0.73-0.92, 95%CI [0.58,0.95], respectively) reliability, and good agreement between moments (mean = -0.07 e - 0.33; LC95% [-2.12; 1.98] and [-3.32; 2.66]) and raters (mean = -0.04 e -0.29; LC95% [-1.42; 1.35] and [-3.27; 2.69]) for total scores, without evidence of systematic bias. SEM and MDC95 ranged from 0.25-0.32 and 0.70-0.88, respectively. Interrater agreement for the COPM’s classification using ICF two-level was almost perfect (k = 0.86). Correlations between COPM and: SGRQ-I and LCADL were significant, negative, and moderate (= -0.47 to -0.65, p < 0.01); lung function and 6MWT were non- significant (p < 0.05), except for performance and 6MWT distance, FEV1 e FVC (= 0.26 to 0.36, p < 0.01) and for satisfaction and FEV1 and FVC (= 0.22 and 0.24, p < 0.05). Floor effects were found in PFSDQ-M. Conclusions: PFSDQ-M and COPM have good reliability and validity indicators to assess HRQoL in Portuguese adults with ILD.