Clinical Predictors of EMG-confirmed Cervical and Lumbosacral Radiculopathy

Background:Electromyography (EMG) for suspected cervical or lumbosacral root compression is often negative, producing expense and physical discomfort that could have been avoided. To improve patient selection for testing, we sought to identify clinical features that would accurately predict presence of radiculopathy on EMG.Methods:Adult patients consecutively evaluated for suspected cervical or lumbosacral root compression at an academic clinical neurophysiology laboratory were prospectively enrolled. Presence of clinical features suggesting root disease (neck or back pain, dermatomal pain or numbness, myotomal weakness, segmental reflex loss, and straight leg-raising) was recorded prior to testing. EMG examination to confirm root compression was conducted per standard protocols. Analysis was based on computation of sensitivity, specificity, predictive values, and accuracy.Results:A total of 200 patients (55% male; mean age 46.4 years; 38% suspected of cervical and 62% of lumbosacral disease) were included. EMG evidence of root disease was detected in 31% of cervical and 62% of lumbosacral referrals. Dermatomal pain was the most sensitive, and segmental reflex loss and myotomal weakness the most specific individual predictors of root disease. Combined presence of dermatomal pain or numbness with segmental reflex loss and myotomal weakness approached specificities of 78% (lumbosacral disease) and 99% (cervical disease). In all cases, myotomal weakness was the most accurate predictor of root disease.Conclusion:The diverse symptoms and signs of cervical and lumbosacral root compression predict a positive electrodiagnosis of radiculopathy with varying degrees of accuracy, and may be used to guide patient selection for EMG testing.

EMG Responses to an Unexpected Load in Fast Movements Are Delayed With an Increase in the Expected Movement Time

When moving an object, the motor system estimates the dynamic properties of the object and then controls the movement using a combination of predictive feedforward control and proprioceptive feedback. In this study, we examined how the feedforward and proprioceptive feedback processes depend on the expected movement task. Subjects made fast elbow flexion movements from an initial position to a target. The experimental protocol included movements made over a short and a long distance against an expected light or heavy inertial load. In each task in a few randomly chosen trials, a motor applied an unexpected viscous load that produced a velocity error, defined as the difference between the expected and unexpected velocities, and electromyographic (EMG) responses. The EMG responses appeared not earlier than 170–250 ms from the agonist EMG onset. Our main finding is that the onset of the EMG responses was correlated with the expected time of peak velocity, which increased for longer distances and larger loads. An analysis of the latency of the EMG responses with respect to the velocity error suggested that the EMG responses were due to segmental reflexes. We conclude that segmental reflex gains are centrally modulated with the time course dependent on the expected movement task. According to this view, the control of fast point-to-point movement is feedforward from the agonist EMG onset until the expected time of peak velocity after which the segmental reflex feedback is briefly facilitated.