Abstract
BackgroundPompe disease is a progressive metabolic myopathy. Involvement of respiratory muscles leads to progressive pulmonary dysfunction, particularly in supine position. Diaphragmatic weakness is considered to be the most important component. Standard spirometry is to some extent indicative but provides too little insight into diaphragmatic dynamics. We used lung MRI to study diaphragmatic and chest-wall movements in Pompe disease.MethodsIn ten adult Pompe patients and six volunteers, we acquired two static spirometer-controlled MRI scans during maximum inspiration and expiration. Images were manually segmented. After normalization for lung size, changes in lung dimensions between inspiration and expiration were used for analysis; normalization was based on the cranial-caudal length ratio (representing vertical diaphragmatic displacement), and the anterior-posterior and left-right length ratios (representing chest-wall movements due to thoracic muscles).ResultsWe observed striking dysfunction of the diaphragm in Pompe patients; in some patients the diaphragm did not show any displacement. Patients had smaller cranial-caudal length ratios than volunteers (p < 0.001), indicating diaphragmatic weakness. This variable strongly correlated with forced vital capacity in supine position (r = 0.88) and postural drop (r = 0.89). While anterior-posterior length ratios also differed between patients and volunteers (p = 0.04), left-right length ratios did not (p = 0.1).ConclusionsMRI is an innovative tool to visualize diaphragmatic dynamics in Pompe patients and to study chest-walland diaphragmatic movements in more detail. Our data indicate that diaphragmatic displacement may be severely disturbed in patients with Pompe disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12890-015-0058-3) contains supplementary material, which is available to authorized users.
Highlights
Pompe disease is a progressive metabolic myopathy
In an earlier study that compared the effects of enzyme replacement therapy (ERT) on pulmonary function in sitting and supine positions, we found that 15% of patients were therapy resistant when pulmonary function was measured in sitting position, and that 35% were therapy resistant when it was measured in supine position [13]
Our study shows that Magnetic resonance imaging (MRI) can be used as an innovative tool to gain greater insight into involvement of the diaphragm in Pompe disease
Summary
Pompe disease is a progressive metabolic myopathy. Involvement of respiratory muscles leads to progressive pulmonary dysfunction, in supine position. We used lung MRI to study diaphragmatic and chest-wall movements in Pompe disease. Pompe disease (OMIM 232300: acid maltase deficiency or glycogen storage disease type II) is an inherited progressive metabolic myopathy caused by acid α-glucosidase deficiency due to mutations in the acid α-glucosidase (GAA) gene (OMIM 606800) [1,2]. Pulmonary dysfunction caused by progressive weakness of the respiratory muscles is a characteristic feature of the disease [1,3,4]. In an earlier study that compared the effects of ERT on pulmonary function in sitting and supine positions, we found that 15% of patients were therapy resistant when pulmonary function was measured in sitting position, and that 35% were therapy resistant when it was measured in supine position [13]. Recent MRI sequences and image analysis techniques make it possible to directly assess the individual contribution of respiratory muscles–including the diaphragm–during the breathing cycle [17,18,19,20,21,22]
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