Identical late motor responses in early Guillain-Barré syndrome: A-waves and Repeater F-waves.

BACKGROUND
Electrodiagnostic (EDx) studies play a key role in the investigation of suspected Guillain-Barré syndrome (GBS), providing diagnostic and prognostic information. However, initial EDx findings may not fulfill neurophysiological criteria for the disease.


AIM
The aim of this study was to estimate the occurrence and characteristics of A-waves and repeaters F-waves (Freps), both late motor responses identical in latency and configuration, in early stages of GBS.


METHOD
We retrospectively analyzed the initial nerve conduction study (NCS) of 26 GBS patients performed within 10 days from symptom onset.


RESULTS
Final subtype diagnosis was acute inflammatory demyelinating polyneuropathy (AIDP) in 16 patients (6 met the criteria at initial EDx study and 10 at follow-up) and acute motor axonal neuropathy (AMAN) in 10 patients (6 initially). Identical late responses were commonly found in the majority of nerves (84%). A-waves were present in 59% and an increased frequency of Freps was calculated in 61% of the 105 studied nerves. A-waves morphology (single or complex) could not distinguish between AIDP and AMAN. Nerves with normal NCS had a significantly higher frequency of A-waves, either isolated or in combination with increased index total Freps, as compared to nerves with low compound muscle action potential (CMAP) amplitudes or conduction block.


INTERPRETATION
Our findings suggest that both late responses can be useful as early markers of conduction changes of various pathophysiology, being frequently present even prior to abnormalities of CMAP parameters.