Content validity and clinical meaningfulness of the HFMSE in spinal muscular atrophy

Abstract

Background: Reports on the clinical meaningfulness of outcome measures in spinal muscular atrophy (SMA) are rare. In this two-part study, our aim was to explore patients' and caregivers' views on the clinical relevance of the Hammersmith Functional Motor Scale Expanded- (HFMSE).

Methods: First, we used focus groups including SMA patients and caregivers to explore their views on the clinical relevance of the individual activities included in the HFMSE. Then we asked caregivers to comment on the clinical relevance of possible changes of HFMSE scores over time. As functional data of individual patients were available, some of the questions were tailored according to their functional level on the HFMSE.

Results: Part 1: Sixty-three individuals participated in the focus groups. This included 30 caregivers, 25 patients and 8 professionals who facilitated the discussion. The caregivers provided a comparison to activities of daily living for each of the HFMSE items. Part 2: One hundred and forty-nine caregivers agreed to complete the questionnaire: in response to a general question, 72% of the caregivers would consider taking part in a clinical trial if the treatment was expected to slow down deterioration, 88% if it would stop deterioration and 97% if the treatment was expected to produce an improvement. Caregivers were informed of the first three items that their child could not achieve on the HFMSE. In response 75% indicated a willingness to take part in a clinical trial if they could achieve at least one of these abilities, 89% if they could achieve two, and 100% if they could achieve more than 2.

Conclusions: Our findings support the use of the HFMSE as a key outcome measure in SMA clinical trials because the individual items and the detected changes have clear content validity and clinical meaningfulness for patients and their caregivers.

Keywords: Carers; Clinical trials; Quality of life; Spinal muscular atrophy.

Fig. 1

Individual responses plotted against age in non-ambulant (gray circle) and ambulant (▲) patients

Fig. 2

Individual responses to the question: ‘Would you agree to have your child take part in a potential trial if, in the absence of side-effects or with possible minimal side-effects, the prospect was to slow down a possible decline in motor function for at least two years?’

Fig. 3

Individual responses to the same question as in fig. 2. Responses are plotted against functional level for non ambulant (gray circle) and ambulant (▲) patients. Functional level is defined both using the raw HFMSE scores and the classification expressing severity in decimals, starting from 2.1, for patients who are just able to sit, to the strongest type 2, 2, who are able to stand but not to walk, to the type 3 [1]

Fig. 4

Individual responses plotted against age and functional level in non-ambulant (gray cirlce) and ambulant (▲) patients