Patient-reported assessment of bulbar function in spinal muscular atrophy (SMA): Validation of a self-report scale

Background: Bulbar dysfunction is a well-recognized burden experienced by individuals with spinal muscular atrophy (SMA). Metrics that capture the impact of these problems are lacking. Objectives: To develop and validate an SMA-Bulbar Scale that captures and quantifies patient-reported experiences with bulbar dysfunction. Methods: Cure SMA database members were invited to complete online surveys and a 31-item Bulbar Scale developed by the authors with reference to both bulbar dysfunction in the literature and consultations with SMA-dedicated health care providers, pharmaceutical companies, and persons affected by SMA. Results: 166 adults with SMA reported a range of bulbar dysfunctions. The most common problems, occurring more than 80% of the time, were prolonged meal times, difficulty with mouth opening, and swallowing pills. In addition, 10% of the respondents reported a worsening feeding function over the course of their lives. Across the diverse array of bulbar functions, exploratory and confirmatory factor analyses of responses identified three coherent dimensions of bulbar dysfunction: Swallowing; Mealtimes and Communication; and Breath Sounds, Speech, Voice, and Secretion Management. Higher scores of overall bulbar dysfunction, (p < .001) and each factor (p < .001), were reported by respondents with any degree of feeding restrictions. Sex, age, or use of SMA disease-modifying treatment did not correlate with bulbar scores. Conclusions: This patient-reported scale of bulbar function in adults with a wide range of SMA severity captures and quantifies the variable manifestations of experienced bulbar impairment. With preliminary evidence of validity, the scale supports efforts to standardize accurate identification of bulbar dysfunction, incorporate the perspectives of people with SMA on key areas of their daily functioning, provide metrics essential for meaningful endpoints in clinical trials, inform practice guidelines, and promote advancement of the regulatory science needed for the evaluation and development of therapeutic interventions. Identification of three coherent dimensions of bulbar dysfunction may improve further investigations.