BACKGROUND AND AIMS: To determine the role of phrenic nerve conduction studies (NCS) in identifying subtypes of Guillain-Barré syndrome (GBS) and to investigate the correlations between phrenic NCS and clinical and respiratory scores. METHODS: A clinical evaluation was conducted on 23 patients diagnosed with GBS, encompassing the Medical Research Council (MRC) sum scores, GBS disability scores, and Erasmus GBS Respiratory Insufficiency Scores (EGRIS). Electrodiagnostic studies (EDX) were conducted twice and bilateral phrenic NCSs once within the 6 weeks after symptom onset. The latency, peak-to-peak amplitude, and negative peak area of phrenic compound muscle action potential (CMAP) elicited using surface electrodes were measured, and the values indicating prolonged latency (≥ 110%-130% of upper limit of normal (ULN)) and/or prolonged negative peak duration (≥ 130% of ULN) were considered as demyelinating. RESULTS: Phrenic NCSs revealed 87.0% sensitivity and 89.5% specificity in the diagnosis of demyelinating subtype (cut-off value of latency 8.6 ms). Most of the phrenic CMAP parameters revealed moderate correlations with clinical scores and with the results of median and ulnar EDX studies. INTERPRETATION: Besides its importance for having correlations with clinical and respiratory features, phrenic NCS may improve the diagnostic sensitivity in differentiating GBS subtypes.
Taşdemir et al. (Mon,) studied this question.