Late-onset Pompe disease (LOPD): may axial myopathy influence respiratory dysfunction?

Background Respiratory dysfunction in Late Onset Pompe Disease (LOPD) is attributed primarily to diaphragm weakness; it is not always proportional to skeletal muscle weakness. Beyond diaphragm and rib cage muscles, we know that posterior trunk muscles participate to inspiration, and abdominal wall muscles contribute to forced expiration. We aimed to investigate whether the involvement of axial muscles detected by muscle MRI may correlate with respiratory dysfunction or influence respiratory functional tests. Methods In 19 patients with LOPD in different stages of disease, we analyzed trunk muscle MRI and upright forced vital capacity FVC, postural drop in VC, and maximal inspiratory and expiratory pressures (MIP, MEP). Results While upright FVC did not correlate with trunk muscle involvement, postural drop in VC, reflecting diaphragm weakness, was strongly influenced by the severity of involvement of all posterior and anterior muscles. Conclusion Trunk muscles involvement in LOPD may reveal respiratory dysfunction and contribute to postural drop in VC. It is likely that axial muscle weakness may impair the compensatory mechanisms occurring in clinostatism, and mainly operated by the abdominal muscles. Detection of axial muscle damage by MRI may thus suggest the need of more extensive respiratory assessment, i.e. by polysomnography, even when upright VC is still within normal ranges.