Why is the EDX evaluation of limited value after a laminectomy

Postoperative EDX studies are of limited value. Abnormalities in the paraspinal muscles are difficult to interpret because denervation potentials can originate from traumatic muscle injury secondary to surgery. Within the first 10 to 14 postoperative days, the EDX study reveals only preexisting abnormalities. Between 3 weeks and 4 months after surgery, EDX results can reliably investigate a previously unsuspected lesion or be used to assess postoperative weakness. When the EDX examination is performed 4 to 6 months after cervical laminectomy or 6 to 12 months after lumbar laminectomy, it is difficult to interpret the significance of findings. Abundant fibrillation potentials found in proximal and distal muscles of the myotome may suggest a recurrent or ongoing radiculopathy.

Key Points

1. Electrodiagnostic evaluation is useful to establish and/or confirm a clinical diagnosis of radiculopathy.

2. EMG has limited usefulness in the evaluation of spinal stenosis.

3. Electrodiagnostic testing should be deferred during the first 2 to 4 weeks following clinical onset of radiculopathy because false-negative studies are common during this time period.

Websites

1. Electrodiagnostic Testing, North American Spine Society: http://www.spine.org/Documents/EMG_2006.pdf

2. Electrodiagnostic Testing, American Academy of Orthopaedic Surgeons: http://orthoinfo.aaos.org/topic.cfm?topic=A00270

3. Practice Guidelines, American Association of Neuromuscular & Electrodiagnostic Medicine: http://www.aanem.org/Practice/ Practice-Guidelines.aspx

BiBLiOGRAPHY

1. Chiodo A, Haig AJ, Yamakawa KS, et al. Magnetic resonance imaging vs. electrodiagnostic root compromise in lumbar spinal stenosis: A masked controlled study. Am J Phys Med Rehabil 2008;87(10):789-97.

2. Dumitru D, editor. Textbook of Electrodiagnostic Medicine. 2nd ed. Philadelphia: Hanley & Belfus; 2001.

3. Lomen-Hoerth C, Aminoff MJ. Clinical neurophysiologic studies: Which test is useful and when? Neurol Clin North Am 1999;17:65-74.

4. Nadin RA, Patel MR, Gudas TF, et al. Electromyography and magnetic resonance imaging in the evaluation of radiculopathy. Muscle Nerve 1999;22:151-55.

5. Pezzin LE, Dillingham TR, Lauder TD, et al. Cervical radiculopathies: Relationship between symptom duration and spontaneous EMG activity. Muscle Nerve 1999;22:1412-18.

6. Robinson LR. Role of neurophysiologic evaluation in diagnosis. J Am Acad Orthop Surg 2000;8:190-99.

7. Spindler HA, Felsenthal G. Electrodiagnostics and spinal disorders. Spine State Art Rev 1995;9:597-610.

8. Streib EW, Sun SF, Paustian FF, et al. Diabetic thoracic radiculopathy: Electrodiagnostic study. Muscle Nerve 1986;9:548-53.

9. Tsao B. The electrodiagnosis of cervical and lumbosacral radiculopathy. Neurol Clin 2007;25(2):473-94.

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