Innovative Measurement and Quantification of the Bell-Shaped Chests of Patients with Spinal Muscular Atrophy: A Pilot Study

Respiratory failure is a major complication in patients with spinal muscular atrophy (SMA) type 1. SMA is manifested by deformation of the chest wall, including one that produces a bell-shaped chest. The aim of this pilot study was to determine the ability of a novel non-ionizing, non-volitional method to measure and quantify bell-shaped chests in patients with SMA. A three-dimensional (3D) depth camera and a chest X-ray (CXR) were used to capture chest images in 14 SMA patients and 28 controls. Euclidean and geodesic chest and abdominal distances were measured from the 3D images and horizontal distances were measured from the CXR images. The ratio of chest distance to abdominal distance was used to quantify chest shape in both groups and were compared between the 3D and CXR methods.. The mean 3D Euclidian ratio of distances was 1.00 in the control group and 0.92 in the SMA group (p = 0.01), the latter indicative of a bell-shaped chest. This result repeated itself in the geodesic measurements (0.99 vs. 0.89, respectively, p = 0.03). There was no difference between the two groups in the ratios of the distances obtained from the CXRs. The herein described novel noninvasive 3D method for measuring chest and abdominal distances was shown to be capable of distinguishing the bell-shaped chest configuration in patients with SMA from the normal chests of controls. This method bears several advantages over CXR and may be easily applicable for use in clinical settings that manage children with SMA.