NATURAL PROGRESSION OF MOTOR FUNCTION IN INDIVIDUALS WITH SPINAL MUSCULAR ATROPHY- ONE YEAR FOLLOW-UP

H.-W. Huang^1,2, J.-Y. Shieh^3,2, W.-C. Weng^4,5,6, F.-Y. Huang^1,2, H.-C. Ho⁷, L.-C. Chen^8,9

¹National Taiwan University Hospital, Division of Physical Therapy, Department of Physical Medicine and Rehabilitation, Taipei, Taiwan, ²National Taiwan University Children Hospital, Child Developmental Assessment and Intervention Center, Taipei, Taiwan, ³National Taiwan University Hospital, Department of Physical Medicine and Rehabilitation, Taipei, Taiwan, ⁴National Taiwan University Hospital, Department of Pediatrics, Taipei, Taiwan, ⁵National Taiwan University, Department of Pediatrics, College of Medicine, Taipei, Taiwan, ⁶National Taiwan University Children Hospital, Department of Pediatric Neurology, Taipei, Taiwan, ⁷Cardinal-Tien Hospital, Department of Physical Medicine and Rehabilitation, New Taipei City, Taiwan, ⁸Fooyin University, Department of Physical Therapy, Kaohsiung, Taiwan, ⁹National Taiwan University, School and Graduate Institute of Physical Therapy, College of Medicine, Taipei, Taiwan

Background: With the rise of disease modifying therapies and new motor assessment instruments for spinal muscular atrophy (SMA), understanding the natural history of motor function progression across SMA type and functional classification is vital for proper interpretation of the treatment effects.

Purpose: This study aimed to document motor functions, using assessment tools specifically designed for SMA, in individuals with SMA type II (SMA-II) and type III (SMA-III) from infancy to adulthood and to investigate the natural progression during 1-year period.

Methods: This was a retrospective study. Medical records were reviewed for patients with SMA from a neuromuscular disorder clinic between July 2019 to September 2020. Individuals with SMA-II or SMA-III who did not undergo disease modifying treatments and received motor function assessments in two clinic visits with one year apart were recruited. This study focused on motor function performance in the Hammersmith Functional Motor Scale- Expanded (HFMSE) and the Revised Upper Limb Module (RULM), two of the most commonly used motor assessments for SMA. Total scores of HFMSE, right and left RULM, and functional classification of participants were retrieved from medical records. Repeated measures ANOVAs were applied to examine the difference of motor scores among SMA types and functional classifications, and to investigate the score change within one year.

Results: A total of 35 individuals with SMA were included in the study. Among the participants, 19 had SMA-II (8 non-sitter; 11 sitter) and 16 had SMA-III (1 non-sitter; 6 sitter; 9 walker). The age at the first motor assessment ranged from 2.7 to 41.9 years (median=14.5 years, SD=9.7 years), with no significant difference between the two types of SMA (P>0.05). Statistical analysis revealed a significant type effect for both HFMSE and RULM results (P<0.001). At both baseline and 1-year follow-up, individuals with SMA-III showed significantly better motor performance than those with SMA-II. The averaged total scores of SMA-III were 27 and 15-16 points higher than SMA-II in HFMSE and RULM, respectively. During the 1-year follow up period, participants showed slight and varied change in HFMSE (0.1±2.0) and RULM (right: 0.6±2.5; left: 0.1±2.5). No significant time or SMA type by time interaction was found (both P>0.05). Investigating the difference among functional classifications, our results indicated that non-sitters, sitters and walkers showed stable motor function during 1-year period.

Conclusions: While individuals with SMA-III showed better motor function than those with SMA-II across age, they both demonstrated relatively stable, rather than declined, motor performance in two most commonly used assessments within one year period.

Implications: Our study findings provide valuable foundation for future studies on effectiveness of SMA therapy. The index of treatment effect for SMA may aim for improvement instead of stability of motor function performance within one year.

Funding acknowledgements: This study was supported by National Taiwan University Hospital research grant (NTUH.110-S4996)

Keywords:
Spinal muscular atrophy
Motor function
Natural history

Topics:
Neurology
Paediatrics
Disability & rehabilitation

Did this work require ethics approval? Yes

Institution: National Taiwan University Hospital

Committee: Research Ethics Committee

Ethics number: 202006215RIND