SMA results in a table of paralysis of varying age onset and severity. It affects all ages including adults. As innovative treatments for SMA are launched, including for adults, the need for sensitive evaluation tools to assess small changes over short periods of time, such as in slowly evolving type III and IV AMS, is important.
For the first time, a longitudinal study, with the participation of the Institute of Myology, was carried out in adults with type III SMA (9 participants) or IV SMA (5 participants) in order to assess the sensitivity of several evaluation tools in disease monitoring. Neuromuscular assessments (muscle strength tests, motor function measurement, quantitative muscle tests, SMAFRS functional scale, etc.), motor unit number estimation (MUNIX) and a quantitative magnetic resonance imaging (MRI) protocol of the cervical spinal cord to assess gray and white atrophy were performed 24 months apart. A composite score was developed based on the three most significant variables.
It emerged that the significant functional decline is:
- most noticeably detected by MUNIX of the abductor of the little finger and anterior tibialis, followed by quantitative muscle tests of flexor muscles of the knee, thumb-index pinch and SMAFRS score,
- least assessed by quantitative cervical MRI (no significant difference),
A significant reduction in the composite score was found to be detectable over the 24-month study. This score, made up of the MUNIX of the abductor of the little finger, the force of the thumb-index pinch and the SMAFRS score, and which integrates both a functional and electrophysiological aspect and a sensitivity to progressive change over time, could be more sensitive than individual measurements.
Reminding that other natural history studies have shown that scores with several measures are better suited to follow a change over time or assess a response to treatment, the authors suggest that the use of this type of evaluation criteria could reduce the number of participants in clinical trials and improve their significance.
Querin G, Lenglet T, Debs R, Stojkovic T, Behin A, Salachas F, Le Forestier N, Amador MDM, Bruneteau G, Laforêt P, Blancho S, Marchand-Pauvert V, Bede P, Hogrel JY, Pradat PF. Development of new outcome measures for adult SMA type III and IV: a multimodal longitudinal study. J Neurol. 2021 Jan 2. doi: 10.1007/s00415-020-10332-5. Epub ahead of print. PMID: 33388927.