Are the neurophysiological techniques useful for the diagnosis of diaphragmatic impairment in multiple sclerosis (MS)?

Objective: To characterize cortico-diaphragmatic pathway involvement in multiple sclerosis (MS) by means of transcranial magnetic stimulation (TMS), and verify its clinical impact. Methods: TMS from diaphragm (Dia), and abductor digiti minimi (AbdV°) was performed in 26 MS patients. Phrenic nerve (PN) conduction study was also performed. Expanded disability status scale (EDSS) and fatigue descriptive scale (FDS) were measured. Forced vital capacity (FVC), forced expiratory volume at the first second (FEV1), peak expiratory flow (PEF) were tested: the predicted percentage value (% pred) was considered. Results: Cortical motor evoked potential (Cx-MEP) latency and central motor conduction time (CMCT) were prolonged, respectively, in 31 and 23% of patients from Dia, in 76 and 79% from AbdV°. PN-compound motor action potential (CMAP) was normal. EDSS correlated to Cx-MEP from AbdV° (P<0.01), and PN-CMAP amplitude (P<0.05), FEV1 % pred (P<0.01), PEF % pred (P<0.01). PN-CMAP amplitude correlated to FVC % pred P=0.05, FEV1 % pred P<0.01, PEF % pred P<0.01. Fatigue was related to AbdV° Cx-MEP and CMCT (P<0.05 and P<0.01). Conclusions: Cortico-diaphragmatic pathway is impaired only in a minority of MS patients. Lack of correlation between TMS findings from Dia and respiratory tests argues against its routinary use to detect subclinical respiratory alterations. Fatigue seems to be related to the motor impairment rather than to respiratory distress.