Phrenic nerve CMAP amplitude, duration, and latency could predict respiratory failure in Guillain-Barre syndrome

To determine the frequency of phrenic nerve abnormalities in Guillain-Barre syndrome (GBS), and evaluate the value of phrenic nerve conduction studies in predicting ventilation failure.

During a study period of one year between July 2008 and July 2009, 28 GBS patients referred to our tertiary university hospital (Alzahra Hospital, Isfahan University of Medical Sciences, Isfahan, Iran) were enrolled in a case control study. Patients with predisposing factors for other polyneuropathies (diabetes mellitus, hypothyroidism, uremia, vitamin deficiency and toxicity) were excluded from the study. Phrenic nerve conduction was studied in the first week after the beginning of symptoms according to the procedure described by Preston and Shapiro.

Diaphragmatic compound muscle action potential (CMAP) latencies, right diaphragmatic CMAP amplitude, and diaphragmatic CMAP duration were significantly different between GBS patients with respiratory failure and without respiratory failure. The CMAP duration was longer in GBS patients with respiratory failure than in the control group (p=0.018), and a CMAP duration of more than 9.6 is an alarm for impending respiratory failure in GBS patients.

Not only phrenic nerve CMAP latency and amplitude, but also diaphragmatic CMAP duration could have predictive value for respiratory failure in GBS patients.