General principles of diagnostic testing as related to painful lumbar spine disorders: a critical appraisal of current diagnostic techniques.

STUDY DESIGN

The literature on diagnostic tests available to the spine clinician for the evaluation of chronic low back pain was reviewed.

OBJECTIVES

To review critically the available information and data on invasive diagnostic tests used for evaluation of chronic low back pain.

SUMMARY OF BACKGROUND INFORMATION

Numerous published studies have described the technique and clinical results of diagnostic blocks for chronic low back pain. There are various methodologies, but most lack of an adequate "gold standard" with which to compare the results of the diagnostic test.

METHODS

The available published studies of diagnostic tests commonly used in the evaluation of chronic low back pain were reviewed, with a focus on invasive techniques. The techniques were evaluated on the basis of the data available to support the conclusions that could be drawn for each of these techniques. The principles of diagnostic testing, including specificity and sensitivity, were reviewed and applied in the context of the data available for each of these invasive tests.

RESULTS

The essential features the clinician seeks in a diagnostic test are accuracy, safety, and reproducibility. It is essential to have a gold standard with which to compare the accuracy of a given diagnostic test. There is no completely reliable gold standard with which to compare a diagnostic test (or injection) when the absence of pain is the end point. The clinical setting in which the test is used directly affects the test results. The prevalence of the disease therefore affects the meaningfulness of the test results. Imaging studies have their greatest value in the exclusion of other conditions. These studies alone were not adequate for predicting the patients who would respond to controlled diagnostic blocks of the facet joint. Facet joint diagnostic blockade probably is most accurately performed by median nerve branch block. The greatest specificity for a positive response to a facet denervation procedure is achieved when the diagnosis is established via highly controlled anesthetic blocks. Over the past few decades, the sacroiliac joint has received varying degrees of interest as an important pain generator of low back pain. Despite testimonials to the contrary, no diagnostic physical examination has correlated with sufficient specificity to diagnose this condition reliably from a clinical standpoint. Lumbar discography has been one of the single most controversial subjects in the management of degenerative, painful lumbar spine conditions. The specificity and sensitivity are high for the diagnosis of disc degeneration. The question that revolves around discography concerns the accuracy of this test for the diagnosis of discogenic pain. An integral part of the problem is the lack of an adequate gold standard. In a comparison of nerve root blockade, sciatic nerve block, posterior ramus block, and subcutaneous injection in a cohort of patients with sciatica, the sensitivity of nerve root block was very high, with only a moderate level of specificity. In the case of diagnostic selective nerve blocks used for evaluation of complex or protean nerve compression, surgical confirmation and clinical results should be a reliable gold standard. Conflicting results have been presented depending on the target lesion and method of study.

CONCLUSIONS

There are inherent limitations in the accuracy of all diagnostic tests. The tests used to diagnose the source of a patient's chronic low back pain require accurate determination of the abolition or reproduction of the patient's painful symptoms.