Ultrasound assessment of diaphragmatic function in type 1 spinal muscular atrophy

Objective: To investigate ultrasound features of diaphragm motion and function in type 1 spinal muscular atrophy (SMA-1) patients. Design: Prospective study. Patients: The study cohort included SMA-1 children younger than 18-year-old. Control subjects included type 2 and type 3 SMA and other neuromuscular disorders younger than 18-year-old. Methodology: Diaphragm ultrasound evaluating diaphragmatic excursion, speed of diaphragmatic contraction, duration of the respiratory cycle, inspiratory/expiratory relationship, end-inspiratory and -expiratory thickness, thickening fraction, and pattern of contractility. The interrater reliability for each variable was established by calculation of Cohen's k coefficient. Results: Twenty-three SMA-1 patients and 12 controls were evaluated. Diaphragm ultrasound values were within normal ranges in all study cohort patients and no difference was found with controls. There was a gradient of diaphragm function with SMA 1.9 subgroup having the best and SMA 1.1 having the worst parameters, particularly in end-inspiratory thickness and diaphragmatic excursion (P =.031 and P =.041, respectively). Seventy-four percent of SMA-1 patients had a dysmotility pattern of diaphragm contraction, mostly represented in SMA 1.9 subgroup (P =.001). This pattern was observed in 92.8% of children on noninvasive ventilation (NIV) for less than 16 hours/d of and in 20% patients with invasive ventilation or NIV for more than 16 hours/d (P =.027). The dysmotility pattern was never observed in the control group. The levels of interobserver agreement were high for “diaphragm irregularities,” “inspiratory/expiratory relationship,” and “diaphragm thickness,” and good for the other variables. Conclusions: Ultrasound can be used to evaluate diaphragm function and contractility in SMA-1 children, providing additional information to the clinical examination and functional respiratory tests, describing a characteristic contractility pattern in these patients. Longitudinal studies are needed to understand the impact of diaphragm dysmotility and other parameters on long-term outcome in SMA-1 patients.