痛みと緩和のジャーナル

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A Reappraisal of The Utility of Needle Electromyography In Low Back Pain: An Observational Retrospective Study

Reynaldo Lazaro and Thomas Eagan

Objective: Needle electromyography (EMG) assesses the function of the motor unit components of the peripheral nervous system. While EMG is effective in evaluating muscle and motor neuron disorders, its value in the assessment of pain per se and of sensory nerve components requires reappraisal. This observational retrospective study, performed by a practicing neurologist and an orthopedic surgeon, examined its utility in the evaluation of low back pain (LBP) with and without neurological symptoms and deficits (NSDs).

Methods: We reviewed the EMG findings concerning 150 patients (100 males, 50 females; age range, 25-65 years) who had been referred by various health care providers for evaluation of post-traumatic LBP. All patients underwent plain radiographs and magnetic resonance imaging (MRI) of the lumbosacral spine, which showed various degrees of intervertebral disc displacements.

EMG examinations were performed from two to six months following the onset of LBP. None of the patients had prior LBP or injury. The patients were categorized into three groups: 1) LBP confined to the lower back or extending to the buttocks or hips (60 patients); 2) LBP associated with unilateral or bilateral sensory symptoms in the thighs or legs, and sometimes the feet, without NSDs (50 patients), and; 3) LBP associated with NSDs in the lower limb, unilaterally or bilaterally (40 patients).

Results: The EMG findings in Group 1 were normal. All but 10 patients in Group 2 showed normal findings. In Group 3, all EMG findings were abnormal, including one patient with cauda equina syndrome secondary to a large herniated disc.

Conclusion: EMG in LBP is predictably abnormal in patients with clear and unequivocal NSDs. EMG for such patients—with or without MRI findings—is debatable, especially if the main disabling symptom is LBP. This study underscores the importance of a good history and a meticulous physical examination to maximize the value of EMG, and to bring awareness to some health care providers that EMG cannot assess low back pain directly, and it only reflects the abnormalities in the motor unit components of the spinal nerve roots.