Validation of quality of life instruments in ALS

Non-invasive ventilation (NIV) probably improves survival in ALS, but its effect on quality of life (QoL) is less clear. Most potentially useful QoL instruments have not been validated in this context.

We assessed the validity (multi-trait multi-method analysis), internal consistency (Cronbach's alpha), test-retest stability (intra-class correlations) and response to disease severity and NIV (effect size) of two generic instruments, the Short Form 36 (SF-36) and the General Well-being Schedule; two specific instruments, the Chronic Respiratory Disease Questionnaire (CRQ) and the Sleep Apnoea QoL Index (SAQLI), and a scale of daytime sleepiness, the Epworth Sleepiness Scale (ESS) in 23 subjects with ALS. Functional status, limb and axial muscle strength, and maximum inspiratory pressure were assessed, together with the QoL measurements, every two months.

All instruments showed good or excellent validity, internal consistency and test-retest stability overall. Subjects without symptomatic respiratory compromise had difficulty identifying activities for the CRQ dyspnoea domain and symptoms for the SAQLI symptoms domain. Marked floor effects were observed in the physical function and role domains of the SF-36. Domains assessing sleep-related problems and mental health showed greater effect of differences in respiratory function than functional status, and the greatest response to NIV.

Of the generic instruments the SF-36 was most useful, but limited by floor effects. Of the specific instruments, the SAQLI symptoms domain was most responsive to NIV, but this instrument took longer to complete, and several items were inappropriate. The CRQ and ESS are valid and responsive alternatives.