Characterization of swallowing biomechanics and function in untreated infants with spinal muscular atrophy: A natural history dataset

Background: Spinal Muscular Atrophy (SMA) is a progressive neuromuscular disorder that in its most severe form, causes profound swallowing deficits. There remains a paucity of research systematically elucidating the biomechanical and functional correlates. This void limits the ability to evaluate the effects of disease-modifying treatments on swallowing. Objective: Elucidate characteristics of swallowing biomechanics and function among untreated patients with SMA. Methods: Infants with SMA who had not received disease modifying therapy when they underwent a videofluoroscopic swallow study (VFSS) were retrospectively identified from 13 international children's hospitals. Infants were eligible if they exhibited symptoms by six months old, or in cases where they detected prior to symptom onset, if they had two copies of SMN2. Eligible infants underwent medical record review to gather oral intake status and need for suctioning for secretion management. Digital files of VFSS’ were extracted and analyzed using BabyVFSSImP™. Non-parametric t-tests were used to compare swallowing biomechanics based on viscosity and the presence of dysphagia symptoms. Results: 62 infants were included in this investigation with average age at initial VFSS 4.4 ± 3.11 months. A high proportion of infants exhibited profound deficits in swallowing biomechanics that impeded extraction of the bolus from the nipple, clearance of the bolus from the pharynx, and prevention of the bolus from entering the airway. Deficits were significantly more prevalent in infants referred for VFSS due to dysphagia symptoms than asymptomatic infants referred as part of high-risk referral (t ≤ 2.5, p ≤ 0.03). A high proportion of infants relied on suctioning for secretion management (34%; N = 21) and alternative nutrition (39%; N = 24), with those relying on these supports exhibiting significantly worse swallowing biomechanics than those who did not (t ≤ 2.8, p ≤ 0.01). Conclusions: Profound deficits in swallowing biomechanics and function are common in infants with SMA. Though clinical symptoms may aid in identifying infants with the most profound swallowing deficits, their absence in cases of more mild deficits inhibits the ability to use these clinical markers as a valid metric of swallowing integrity.