Sleep-disordered breathing and respiratory failure in acid maltase deficiency

Background: Sleep-disordered breathing (SDB) and respiratory failure (RF) are complications of acid maltase deficiency (AMD), a rare hereditary myopathy. Objective: To define the relationship between lung and respiratory muscle function, to establish incidence and patterns of SDB, and to determine daytime predictors of SDB. Methods: Sitting and supine lung and respiratory muscle function tests were obtained in 27 subjects with juvenile and adult AMD (aged 39 +/- 19 years) and compared with outcomes of polysomnography. Results: Ventilatory restriction was present in 17/27 subjects. Inspiratory vital capacity (IVC) correlated (p < 0.005) with peak inspiratory muscle pressure (PIP, R = 0.61), respiratory muscle strain (P-0.1/P-0.1max, R = -0.68), and gas exchange by day (PaO2: R = 0.71; PaCO2: R = -0.64) and night (SaO(2): R = 0.73; PtcCO2: R = -0.75). Diaphragm weakness (DW) was present in 13 subjects, 10 of whom had hypercapnic RF (PaCO2 65 +/- 7 min Hg), and was associated with longer disease course. SDB was found in 13 subjects, 12 with DW. It was characterized by REM-sleep hypopneas that, as ventilatory restriction worsened, were complemented by hypoventilation (PtcCO2 > 50 min Hg) first in REM sleep, then in non-REM sleep (p < 0.005). SDB was predicted by DW (sensitivity 80%, specificity 86%) and nocturnal hypoventilation by IVC < 40% (sensitivity 80%, specificity 93%). Noninvasive ventilation, instituted for daytime respiratory failure or nocturnal hypoventilation, normalized daytime and nocturnal gas exchange (p < 0.005). Conclusion: Vital capacity correlates with respiratory muscle function in AMD. Diaphragm weakness is the major cause of SDB and RF. SDB and nocturnal hypoventilation are predictable from daytime function tests.