Objective:

Development of new parameters for earlier prediction and more specific presentation of development of critical illness myopathy(CIM).

Background:

CIM is most common cause of ICU-acquired muscle weakness. In electrophysiological diagnosis, synchronous dispersion observed in distal and proximal stimulation in CMAP negative-peak-time(NP_Duration), which has a high diagnostic value, cannot be observed in some patients or is at borderline. Based on our observation that "prolongation of NP_Duration is more evident at low stimulation-intensities", NP_Duration at submaximal stimulation-intensities and contribution to diagnosis of CIM were examined.

Design/Methods:

Study was conducted with ulnar nerve stimulation and recording from ADM muscle in 11 patients diagnosed with CIM after EMG and 12 healthy individuals.  Maximal-stimulation-intensity(S_Max), and minimal(S_Min) at which first muscle action potential was detected, were determined.By dividing S_Max–S_Min range into 4 equal parts, 6 percentage stimulation-intensities(S_Min,S_%20,S_%40,S_%60,S_%80,S_Max) were determined. Amplitude of CMAPs(Amp_S_x) and NP_Duration(Duration_S_x) and ratio of NP_Duration at each stimulation-intensity to Duration_S_Max(MaxRatio_Duration_S_X) were calculated. 2-level[STIMULATION-VIOLENCEXGROUP]repeated-measures ANOVA was applied in analysis.

Results:

In patient group, Amp_S_60%, Amp_S_80% and Amp_S_Max values were significantly lower(p=0.002,p=0.000,p=0.032). NP_Duration was significantly longer in patient group than in control group at all stimulation-intensities(p=0.000). However, in 2 patients(18%), NP_Duration was longer than normal only in S_min and S_%20. Moreover, in patient group, NP_Duration was maximum at S_Min intensity and gradually shortened as stimulation-intensity increased, while in healthy individuals it was vice versa. Consistent with this finding, MaxRatio_Duration_S_Min and MaxRatio_Duration_S_%20 in patient group were significantly higher than in control group(p=0.000, p=0.000).

Conclusions:

Prolongation of NP_Duration, which has electrophysiological-diagnostic value for CIM, was detected with higher sensitivity at S_Min and S_%20 stimulation-intensities which can be performed in a short time, compared to supramaximal stimulation-intensity used in routine examinations. It was thought that this new finding was due to difference in muscle fibers stimulated at different stimulation intensities and phase-cancellation and would increase true-positivity in the early stages of CIM.