Determination of the Minimal Clinically Important Difference Scores for the Cystic Fibrosis Questionnaire-Revised Respiratory Symptom Scale in Two Populations of Patients With Cystic Fibrosis and Chronic Pseudomonas aeruginosa Airway Infection
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Abstract
The Cystic Fibrosis Questionnaire-Revised (CFQ-R) is a validated patient-reported
outcome (PRO) containing both generic scales and scales specific to cystic fibrosis
(CF). The minimal clinically important difference (MCID) score for a PRO corresponds
to the smallest clinically relevant change a patient can detect. MCID scores for the
CFQ-R respiratory symptom (CFQ-R-Respiratory) scale were determined using data from
two 28 day, open-label, tobramycin inhalation solution (TIS) studies in patients with
CF and chronic Pseudomonas aeruginosa airway infection. At study enrollment, patients
in the study 1-exacerbation had symptoms indicative of pulmonary exacerbation (n =
84; < 14 years of age, 31 patients; > or = 14 years of age, 53 patients); patients
in study 2-stable had stable respiratory symptoms (n = 140; < 14 years of age, 14
patients; > or = 14 years, 126 patients).
The anchor-based method utilized a global rating-of-change questionnaire (GRCQ) that
assessed patients' perceptions of change in their respiratory symptoms after TIS treatment.
The mean change from baseline CFQ-R-Respiratory scores were mapped onto the GRCQ to
estimate the MCID. The two distribution-based methods were as follows: (1) 0.5 SD
of mean change in CFQ-R-Respiratory scores (baseline to end of TIS treatment); and
(2) 1 SEM for baseline CFQ-R-Respiratory scores. Triangulation of these three estimates
defined the MCIDs.
MCID scores were larger for patients in study 1-exacerbation (8.5 points) than for
those in study 2-stable (4.0 points), likely reflecting differences in patient disease
status (exacerbation/stable) between these studies.
Patient benefit from new and current CF therapies can be evaluated using changes in
CFQ-R-Respiratory scores. Using the MCID provides a systematic way to interpret these
changes, and facilitates the identification of CF treatments that improve both symptoms
and physiologic variables, potentially leading to better treatment adherence and clinical
outcomes. Trial registration (study 1-exacerbation): Australian-New Zealand Clinical
Trials Registry Identifier: ACTRN 12605000602628 Trial registration (study 2-stable):
ClinicalTrials.gov Identifier: NCT00104520.