Dyspnea in Amyotrophic Lateral Sclerosis: Rasch-Based Development and Validation of a Patient-Reported Outcome (DALS-15).

Abstract

Dyspnea is a cardinal but often underestimated symptom in amyotrophic lateral sclerosis (ALS). The lack of a satisfying assessment tool leads to diagnostic uncertainty and bears the risk that established life-prolonging and symptom-relieving therapeutic options will not be adequately applied. The objective of this study was to develop and validate a German language disease-specific patient-reported outcome measure to assess dyspnea in ALS by combination of a qualitative and quantitative approach using Rasch analysis. Based on input from clinical experts and patients, a preliminary 35-item questionnaire was developed and completed by 94 patients with ALS having dyspnea. Data were subjected to Rasch analysis and tested for required measurement issues such as appropriate response categories, the absence of differential item functioning, local independence, and unidimensionality. After iterative Rasch analyses, the final 15-item Dyspnea-ALS-Scale (DALS-15) was obtained. The scale satisfies the axioms of the Rasch model with good fit statistics, the absence of local dependency, and differential item functioning as well as acceptable unidimensionality. The DALS-15 is optimally targeted and suitable for group and individual use. It shows excellent test-retest reliability and convergent validity. The DALS-15 satisfies strictest modern measurement criteria and has interval scale properties. It fills an important gap in assessment and could be most helpful to optimize symptom management in patients with ALS.