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When it comes to back pain, psychological distress is a more reliable predictor of the problem than imaging and diagnostic disc injection, Stanford University School of Medicine researchers say. Their finding could affect how doctors treat back pain, which often includes costly surgery that insurance companies are increasingly reluctant to cover.
Most adults in the United States will experience disabling lower back pain at least once in their lives, but their doctors frequently can't find a specific physical cause. In a four-year investigation that followed patients who initially had no lower back pain, researchers studied their subjects' spines using both disc injection and magnetic resonance imaging, or MRI. And they also got to know their research subjects through psychological evaluations. It turned out that psychological factors more accurately predicted who would develop lower back pain than the two diagnostic techniques.
In people both with and without back pain, MRI can detect cracks or tears in the spongy cartilage disc that cushions each unit of the spine. Some doctors also have suggested that if a patient feels pain when fluid is injected into one of the spine's discs in a procedure called discography, the patient will soon develop back pain even if he or she doesn't already feel discomfort.
“It was thought that discography could separate the wheat from the chaff,” said Eugene Carragee, MD, professor of orthopedic surgery and lead author of the study, which is published in the May 15 issue of Spine. “But the bottom line is that it didn't predict who would go on to develop back pain.” Carragee and colleagues also found that the invasive discography procedure itself does not injure the spinal disc enough to cause back pain.
Carragee and his team examined 46 discography subjects and 49 control individuals annually over the four-year study period. Some of them had undergone cervical surgery or had been diagnosed with chronic pain syndrome, but none had lower back pain at the start of the study. “Nobody had ever followed a high-risk, asymptomatic group with discography or MRI for such a long period,” said Carragee, who also directs Stanford's Orthopedic Spine Center.
The researchers found that patients with poor coping skills – as measured by psychological testing – or with chronic pain were nearly three times more likely to develop back pain compared to those with neither. A history of disputed workers' compensation claims also predicted future back pain. Meanwhile, a crack in the disc or a “high-intensity zone” seen on MRI was weakly associated with back pain, but the result was not statistically significant. “The structural problems were really overwhelmed by the psychosocial factors,” Carragee said. [Emphasis added.]
Some insurance companies and state workers' compensation funds are already balking at paying for surgery to treat nonspecific back pain associated with psychosocial problems, he noted. Only a quarter of the 300,000 spinal fusion operations that occur each year are done for obvious reasons, such as tumors, infections or deformities, and just a fraction of the rest – those with pain and ordinary age-related degeneration – have good results from the surgery.
“The question is, can we better identify groups that have a greater chance of being helped by surgery?” Carragee asked. It may be more appropriate to treat other patients by helping them cope with the pain and strengthening their backs, he suggested.
Prospective
controlled study of the development of lower back pain in previously asymptomatic
subjects undergoing experimental discography.
Carragee EJ, Barcohana B, Alamin T, van den Haak E.
Orthopaedic Surgery Department, Stanford University, Stanford,
CA 94305, USA. carragee@stanford.edu
STUDY DESIGN : A prospective controlled longitudinal study.
OBJECTIVES: To determine whether subjects, asymptomatic for lower back problems, who undergo experimental discography, will develop lower back problems during the medium term to the full term.
SUMMARY OF BACKGROUND DATA: Previous work has shown significant pain on discographic injection in approximately 40% of asymptomatic subjects. It has been suggested that those subjects with painful injections would soon develop lower back pain (LBP) syndromes in the near future: that is, the experimental discography was detecting an imminent "pain generator" before clinically symptomatic.
METHODS: Fifty subjects without low back pain were recruited for clinical and psychometric testing, MRI scanning, and experimental lumbar discography to determine the rate of painful lumbar disc injections in select subjects without LBP history. After determining which subjects had painful injections, all subjects completing the discography protocol were prospectively followed at yearly intervals to determine the occurrence of LBP and LBP disability over time. Statistical methods were then used to determine the correlation, if any, between the asymptomatic subjects' clinical, MRI, and discography findings, and the subsequent LBP measures. Controls, not participating in the lumbar discography study, were also followed. Controls were matched for clinical features, sex, age, and occupational/recreational exposure. Follow-up examinations were performed at yearly intervals by blinded researchers using a scripted interview and completing standard questionnaires.
RESULTS: A total of 46 of 50 completed the discogram, and all 46 subjects completed the final 4-year follow-up examination. There was a low incidence of LBP episodes in the experimental groups and control. A painful disc injection, independent of psychological profile, did not predict LBP or any other functional outcome measure at follow-up on multivariate analysis. The presence of an anular fissure seen on discography was weakly associated with the cumulative incidence of LBP episodes after discography (P = 0.08). The presence of high intensity zone on MRI in any disc was also weakly associated with the development of LBP episodes (P = 0.09). Psychometric profiles at the start of the study strongly and independently predicted future back pain (P = 0.01), medication usage (P = 0.002), and work loss (P = 0.01) over the 4-year study. Compared with controls not having undergone discography, there was no significant difference in back pain, function, work loss, doctors visits for back pain, or medication intake in any group. A subset in the injection group with somatization disorder had a higher LBP visual analog score compared with somatization disorder controls at 1 year,but this was not significant at 4 years after testing.
CONCLUSIONS:
Painful disc injections are poor independent predictors of subsequent
LBP episodes in subjects initially without active lower back complaints. Anular
disruption is a weak predictor of future LBP problems. Psychological distress
and preexisting chronic pain processes are stronger predictors of LBP outcomes.
PMID: 15131439 [PubMed - in process]
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