Repetitive nerve stimulation for the evaluation of peripheral nerve hyperexcitability.
OBJECTIVE
To examine the utility of repetitive nerve stimulation (RNS) in the evaluation of peripheral nerve hyperexcitability (PNH).


BACKGROUND
PNH describes a group of disorders characterized by muscle cramps, twitching and stiffness. When severe, PNH may be characterized by the presence of continuous muscle fiber activity on routine needle electromyography (EMG). In milder forms of the disease, nerve hyperexcitability may be evidenced by the presence of after-discharges or cramp potentials following RNS.


METHODS
Fifty-four patients were prospectively recruited and classified into one of three groups-PNH, other neuromuscular disease and controls. We recorded and quantified the after-discharges and cramp potentials following RNS at 1, 5, 10 and 30 Hz.


RESULTS
The proportion of nerves with after-discharges and/or cramp potentials was significantly greater in the PNH group than the control group at both 5 Hz (p=0.03) and 10 Hz (p=0.01), as well as in the neuromuscular disease group compared to controls at 5 Hz (p=0.02). There was also a significant concordance between complaints of muscle cramps and fasciculations and the finding of after-discharges and/or cramp potentials at both 5 Hz (p=0.005) and 10 Hz (p=0.004). At a stimulation frequency of 10 Hz, the sensitivity of RNS for the diagnosis of PNH (primary or secondary) was 79% and the specificity was 88%.


CONCLUSIONS
Our findings suggest that RNS at or below a stimulation frequency of 10 Hz (when positive) is a useful test for the diagnosis of PNH, whether it is primary or secondary.
Benatar
Michael
M
Department of Neurology, Emory University, 1365A Clifton Road N.E., Atlanta, GA 30322, USA. mbenata@emory.edu
Chapman
Kristine M
KM
Rutkove
Seward B
SB
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004558:Electric Stimulation; D004576:Electromyography; D005207:Fasciculation / Q000503:physiopathology; D006801:Humans; D008875:Middle Aged; D009120:Muscle Cramp / Q000503:physiopathology; D009468:Neuromuscular Diseases / Q000503:physiopathology; D017933:Peripheral Nervous System / Q000502:physiology / Q000503:physiopathology; D010523:Peripheral Nervous System Diseases / Q000175:diagnosis / Q000503:physiopathology*; D012016:Reference Values; D012680:Sensitivity and Specificity