Relationship between respiratory function and need for NIV in childhood SMA

BACKGROUND: Spinal muscular atrophy (SMA) causes progressive respiratory muscle weakness but respiratory function (RF) in those using noninvasive ventilation (NIV) is not well described. OBJECTIVE: To describe RF in childhood SMA and assess differences between those using and not using NIV. METHODS: A cross‐sectional study of childhood SMA assessed polysomnography (PSG), spirometry, forced oscillation technique (FOT), lung clearance index (LCI), sniff nasal inspiratory pressures, peak cough flow, maximal inspiratory and expiratory pressure, and NIV use and indication. RESULTS: Twenty‐five children (median age [interquartile range], 8.96 [5.63] years; 10 F) with SMA 1 (n = 3), 2 (n = 15), and 3 (n = 7) were recruited. Spirometry and FOT testing was feasible in children as young as 3 years. Ten (40%) required NIV, 5 for sleep‐disordered breathing (SDB), and 5 initiated during lower respiratory tract infection (LRTI). Children requiring NIV were older (median, 10.52 vs 5.67 years; P < .02) with more abnormal forced vital capacity (FVC) z‐score (−5.70 vs −1.39, P < .02), Rsr8 z‐score (1.97 vs 0.50, P = .04), and LCI (8.84 vs 7.34, P = .01). Two had normal RF and SDB. For FVC z‐score less than −2.5 and LCI greater than 7.5, the odds ratio for NIV was 10.70 (95% confidence interval [CI], 1.39‐82.03) and 2 (95% CI, 0.40‐10.31), respectively. All children with LCI greater than 8 used NIV. FVC z‐score and LCI are associated with maximum transcutaneous carbon dioxide on PSG (r = 0.43, P < .001). CONCLUSION: NIV is common in SMA. Normal RF does not exclude SDB. Children with more abnormal FVC and LCI should be considered at risk of starting NIV during/following an LRTI.