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Special Studies - CT/MRI/Myelog - Efficacy

Lumbar disc herniation. 17 articles used surgical findings as the gold standard. Four evaluated plain myelography alone and found a true positive rate of 75-94%, and a true negative rate of 55-100%. Eight evaluated CT compared with myelography. All reported similar ranges of true positive 60-91% CT; 65-98% myelography; and true negative 57-100% for CT and 43-100% myelography.

One study looked at the added diagnostic value of CT & myelography. The probability of detecting a true lumbar disc herniation on imaging is 77% with one test, and 91% if both done. Probability of an imaging test showing a false positive is 17% to 28% if one test is positive, but approaches zero if both are positive. The five remaining articles evaluated multiple imaging tests. These studies all found no significant differences between CT, MRI and CT-myelography in terms of their true positive rates and true negative rates for diagnosing lumbar disc herniation although all these tests were better than plain myelography. Jackson et al. report that CT-discography had a greater true positive rate (92%) than either CT-myelography, plain CT or plain myelography or plain discography. However they recommend MRI over other imaging tests.

Spinal stenosis. The panel reviewed one meta analysis on the accuracy of CT, MRI and myelography for diagnosing lumbar spinal stenosis in adults. The authors conclude that estimates of accuracy of these imaging tests were imprecise, and likely too high, but based on the data available the meta-analysis found both CT and MRI were of similar accuracy. Plain myelography had lower accuracy.

Asymptomatic subjects. In one paper evaluating CT scans in only asymptomatic individuals, disc herniation was diagnosed in 19.5% in subjects <40 years of age and 50% in subjects >40.

For MRI diagnoses found: any abnormality, 30-57%, bulging discs, 56-79%; disc herniation, 17-36%; disc degeneration, 34-93%; spinal stenosis, 0-21%--with the highest findings in the >60 age group.

In 302 asymptomatic women found 34% degenerative discs age 21-30 and increasing to 95% by age 70.

MRI in 20 year old males found 57% disc degeneration in 75 subjects with LBP and 35% disc degeneration in 34 subjects without LBP.

A herniated disc noted on an imaging test is more likely to be associated with a clinically significant nerve root compromise in patients when there are other findings that suggest physiologic nerve root compromise.

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