INTRODUCTION/AIMS: The leading clinical feature of 5q-associated spinal muscular atrophy (SMA) is symmetric, proximal muscle weakness. Muscles involved in ventilation exhibit a specific pattern of denervation: intercostal muscles are severely atrophic, whereas the diaphragm muscle is less affected. The aim of this study was to investigate the involvement of diaphragmatic function by ultrasound imaging in adult patients with SMA and to quantify dynamics of diaphragmatic function during nusinersen treatment.

METHODS: Diaphragmatic thickness, thickening, and excursion during quiet breathing were assessed in 24 adult patients with SMA type 2 and 3 by diaphragm ultrasound imaging before and during nusinersen treatment and were correlated with spirometric parameters.

RESULTS: Diaphragm thickness was not reduced, but increased in a remarkable proportion of patients, whereas diaphragm thickening and excursion were reduced in about 20% to 30% of nusinersen-naive, adult patients with SMA types 2 and 3. During 26 months of nusinersen treatment, diaphragm thickening fraction and excursion improved.

DISCUSSION: Diaphragm ultrasound imaging can provide disease- and treatment-relevant information that is not identified during routine clinical assessments and may therefore be a valuable complementary outcome measure.