Respiratory muscle weakness in facioscapulohumeral muscular dystrophy

Introduction The purpose of this study was to comprehensively evaluate respiratory muscle function in adults with facioscapulohumeral muscular dystrophy (FSHD). Methods Fourteen patients with FSHD (9 men, 53 +/- 16 years of age) and 14 matched controls underwent spirometry, diaphragm ultrasound, and measurement of twitch gastric and transdiaphragmatic pressures (twPgas and twPdi; n = 10) after magnetic stimulation of the lower thoracic nerve roots and the phrenic nerves. The latter was combined with recording of diaphragm compound muscle action potentials (CMAPs; n = 14). Results The following parameters were significantly lower in patients vs controls: forced vital capacity (FVC); maximum inspiratory and expiratory pressure; peak cough flow; diaphragm excursion amplitude; and thickening ratio on ultrasound, twPdi (11 +/- 5 vs 20 +/- 6 cmH(2)O) and twPgas (7 +/- 3 vs 25 +/- 20 cmH(2)O). Diaphragm CMAP showed no group differences. FVC correlated inversely with the clinical severity scale score (r = -0.63, P = .02). Discussion In FSHD, respiratory muscle weakness involves both the diaphragm and the expiratory abdominal muscles.