The motor and functional scales most commonly used to assess adult patients with spinal muscular atrophy (SMA) have both strengths and limitations when evaluating these patients.
When comparing motor functional scales, including the Hammersmith Functional Motor Scale Expanded (HFMSE) and the Revised Upper Limb Module (RULM), with bedside functional scales, including Egen Klassification (EK2) and the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R), bedside functional scales had some advantages, according to a study published in the European Journal of Neurology.
According to the study authors, the bedside functional scales were generally faster, cheaper, and easier to administer to patients. The bedside scales could also distinguish a greater range of functional states than the motor scales, which tended to show ceiling and floor effects.
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The inclusion of nonmotor items important to patients, such as fatigue or respiratory problems, as well as a more direct insight into the clinical relevance of a score change for an individual patient were also benefits of bedside scales. Additionally, bedside functional scales that are self-administered or telematically administered have been shown in previous studies to be reliable and reproducible.
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During the study, 79 patients with SMA were enrolled, and the HFMSE, RULM, EK2, and ALSFRS-R scores were recorded in addition to the 6-minute walk test (6MWT) and the percent-predicted forced vital capacity (FVC%). All 4 functional scales showed strong to very strong correlations with one another.
“Until now, motor function scales (such as 6MWT, HFMSE, and RULM) are those most frequently used in adult SMA patients to assess the efficacy of nusinersen. However, most of them have been designed and validated in children, and children present considerable differences (eg, in disease progression rate, contractures and scoliosis, comorbidities, etc) with adults that could affect their validity and responsiveness,” the authors said.
The patients were divided into functional subgroups including walkers (patients who could walk at least 5 steps without assistance), sitters (who could sit without assistance or head support for more than 10 seconds), and nonsitters.
Of the tests applicable to all 3 subgroups, ALSFRS-R showed the strongest discriminating ability (Bangdiwala’s concordance test [B]=0.72). HFMSE showed strong discriminating ability between walkers and sitters (B=0.86), while EK2 could distinguish between sitters and nonsitters (B=0.68).
In regard to responsiveness to nusinersen treatment, both the bedside and motor scales only showed low to moderate internal responsiveness in patients. Responsiveness was higher overall with the bedside functional scales than with the motor scales, however, which has also been observed in a previous study. The authors did mention that both this study and the previous study had small sample sizes and that the responsiveness results should be interpreted with caution.
“New outcome measures, applicable and responsive to all functional subgroups, should probably be developed. Until then, the combined use of several outcome measures will be needed,” the authors concluded.
Reference
Vázquez-Costa JF, Povedano M, Nascimiento-Osorio AE, et al. Validation of motor and functional scales for the evaluation of adult patients with 5q spinal muscular atrophy. Eur J Neurol. Published online September 1, 2022. doi:10.1111/ene.15542
