Myelography, Discography and Selective Neural Blockade
Diagnostic Tools to Optimize Outcome in Low Back Pain: Part 3
A myelogram involves penetration of the subarachnoid space and is generally not indicated in the evaluation of acute low back pain. It is generally reserved as a preoperative test, often in conjunction with a CT scan. This provides a detailed, anatomic picture, particularly of the spinal osseous elements and can be used to correlate examination findings and assist in pre-operative planning. It is rarely used in the physiatric evaluation of patients with acute low back pain except in cases where the clinical picture supports a progressive neurologic deficit and the MRI and EMG are nondiagnostic.
Discography is rarely necessary in the evaluation of acute low back pain and certainly not recommended within the first 3 months of treatment. It can be helpful such as patients who have not responded to a well-coordinated rehabilitation program or who have normal or equivocal MRI findings. In such cases, it may have some benefit in localizing a symptomatic disc as the etiology of nonradicular back pain.
A positive discogram must include a concordant pain response. This includes reproduction of symptoms upon injection into a symptomatic disc; a non-painful response upon injection of control discs, and observed annular pathology on post discography CT scanning if utilized. Discography is most often used prior to contemplating surgical fusion for unremitting pain due to a symptomatic internal disc disruption. Some have found discography followed by CT to be a more precise technique and may delineate discovertebral pathology with sensitivities similar to or better than MRI and CT/myelography. It is the only quasi-objective provocative test for disc-mediated pain.
Diagnostic Selective Neural Blockade
Diagnostic selective nerve root injection is also rarely necessary in the evaluation of acute low back pain. It is indicated in patients with radicular symptoms who have not responded to a previously employed comprehensive rehabilitation program, which may have included oral or translaminar injections of epidural steroid. It is helpful in determining a symptomatic nerve root when other studies (e.g. EMG) have been equivocal, and in determining whether therapeutic nerve root injections might be helpful.
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