Phrenic nerve involvement and respiratory muscle weakness in patients with Charcot-Marie-Tooth disease 1A

Diaphragm weakness in Charcot-Marie-Tooth disease 1A (CMT1A) is usually associated with severe disease manifestation. This study comprehensively investigated phrenic nerve conductivity, inspiratory and expiratory muscle function in ambulatory CMT1A patients. Nineteen adults with CMT1A (13 females, 47 +/- 12 years) underwent spiromanometry, diaphragm ultrasound, and magnetic stimulation of the phrenic nerves and the lower thoracic nerve roots, with recording of diaphragm compound muscle action potentials (dCMAP, n = 15), transdiaphragmatic and gastric pressures (twPdi and twPgas, n = 12). Diaphragm motor evoked potentials (dMEP, n = 15) were recorded following cortical magnetic stimulation. Patients had not been selected for respiratory complaints. Disease severity was assessed using the CMT Neuropathy Scale version 2 (CMT-NSv2). Healthy control subjects were matched for age, sex, and body mass index. The following parameters were significantly lower in CMT1A patients than in controls (all P < .05): forced vital capacity (91 +/- 16 vs 110 +/- 15% predicted), maximum inspiratory pressure (68 +/- 22 vs 88 +/- 29 cmH(2)O), maximum expiratory pressure (91 +/- 23 vs 123 +/- 24 cmH(2)O), and peak cough flow (377 +/- 135 vs 492 +/- 130 L/min). In CMT1A patients, dMEP and dCMAP were delayed. Patients vs controls showed lower diaphragm excursion (5 +/- 2 vs 8 +/- 2 cm), diaphragm thickening ratio (DTR, 1.9 [1.6-2.2] vs 2.5 [2.1-3.1]), and twPdi (8 +/- 6 vs 19 +/- 7 cmH(2)O; all P < .05). DTR inversely correlated with the CMT-NSv2 score (r = -.59, P = .02). There was no group difference in twPgas following abdominal muscle stimulation. Ambulatory CMT1A patients may show phrenic nerve involvement and reduced respiratory muscle strength. Respiratory muscle weakness can be attributed to diaphragm dysfunction alone. It relates to neurological impairment and likely reflects a disease continuum.