Dysphagia Phenotypes in Spinal Muscular Atrophy: The Past, Present, and Promise for the Future

Abstract

Purpose The aim of this study was to provide clinicians with an overview of literature relating to dysphagia in spinal muscular atrophy (SMA) to guide assessment and treatment. Method In this clinical focus article, we review literature published in Scopus and PubMed between 1990 and 2020 pertaining to dysphagia in SMA across the life span. Original research articles that were published in English were included. Searches were conducted within four themes of inquiry: (a) etiology and phenotypes, (b) respiratory systemic deficits and management, (c) characteristics of natural history dysphagia and its treatment, and (d) dysphagia outcomes with disease-modifying therapies. Articles for the first two themes were selected by content experts who identified the most salient articles that would provide clinicians foundational background knowledge about SMA. Articles for the third theme were identified using search terms, including spinal muscular atrophy, swallow, dysphagia, bulbar, nutrition, g-tube, alternative nutrition, jaw, mouth, palate, OR mandible. Search terms for the fourth theme included spinal muscular atrophy AND nusinersen OR AVXS-101/onasemnogene abeparvovec-xioi. Review of Pertinent Literature Twenty-nine articles were identified. Findings across identified articles support the fact that patients with SMA who do not receive disease-modifying therapy exhibit clinically significant deficits in oropharyngeal swallow function. Few investigations provided systematic information regarding the underlying physiological deficits responsible for this loss in function, the timing of the degradation, or how disease-modifying therapies change these outcomes. Conclusion Future research outlining the physiological and functional oropharyngeal swallowing deficits among patients with SMA who receive disease-modifying therapy is critical in developing standards of dysphagia care to guide clinicians.

Figure 1.

Healthy normal individuals have two copies of SMN1 that produce the majority of functional spinal motor neuron protein necessary for motor neuron survival. Patients with SMA have mutations or deletions in both SMN1 genes that inhibit sufficient production of functional spinal motor neuron protein.

Figure 2.

Bell-shaped chest resulting from insufficient intercostal muscle strength preventing against inward paradoxical rib cage prolapse during inspiration.

Figure 3.

Fluoroscopic visualization of maximum pharyngeal contraction during swallowing in (1) a healthy normal infant and an (2) infant with spinal muscular atrophy 1. Infant with spinal muscular atrophy Type 1 has incomplete (a) soft palate elevation, (b) tongue base retraction, (c) pharyngeal stripping wave, (d) epiglottic inversion, and (e) upper esophageal segment opening resulting in no clearance of bolus from the pharynx (residue).

Figure 4.

Fluoroscopic visualization of pharynx after the swallowing in (1) a healthy young adult and a (2) young adult with spinal muscular atrophy (SMA) Type III. Adult with SMA Type III has (a) pyriform and (b) vallecular residue, as indicated by arrows after the swallow, whereas the healthy normal adult has no segment opening resulting in no clearance of bolus from the pharynx (residue). Note the retracted neck posture in the patient with SMA.