With the emergence of effective disease-modifying treatments (DMTs), the conventional “type” classification and spinal muscular atrophy (SMA) that was based upon features of the untreated natural history is now outdated. Following DMT, patients no longer steadily decline after gains associated with development reach a maximum; instead, they either continue to gain motor abilities throughout normal development, or if treated after the onset of progressive decline, they stabilize against further decline. A new ordinal classification scale of functionally important items is thus necessary to address the evolving clinical and research issues associated with this new natural history. The scale, Functional Ability Scale for Evolving Spinal Muscular Atrophy (EVOLVE-SMA), addresses the need for a broader classification of SMA, offering potential benefits such as enhanced therapy assessment, refined clinical trials criteria, biomarker development, and population-based therapy impact assessment. We describe the stages of development of a new ordinal scale of functionally important abilities intended to serve both clinical and research purposes. To be of value, a new scale must satisfy multiple dimensions: maximum granularity of functional levels with minimal sacrifice of reliability, meaningfulness by assessing functionally important tasks, broad range of applicability, and measurable consistency of assessment between naive and experienced clinicians and people with SMA and their caregivers without any specific training that would be subject to temporal decline.
