Department of Rheumatology, Morriston Hospital, Swansea SA6 6NL, UK
SIR, I was interested in the reported trial of Dechow et al. [1] as much for the treatment modality as the negative outcome. In trying to explain why there were no differences in the outcome measures used between the control and the sclerosant injection groups, the authors concluded their discussion by asking whether there might be subgroups of low back pain patients who might be more likely to respond to that particular treatment.
Indeed, this may explain why so many previous trials have failed to show much evidence of effect for almost all forms of treatment of back pain. It was for this very reason that a combined therapeutic trial and classification analysis [2] was undertaken, which likewise was to show no obvious treatment effects when all patients were lumped together. However, subgroups were distinguished and it was thus possible to show diagnosis-related response to treatment and also to show which outcome criteria were effective in distinguishing the differing responses [3].
The most recent discussion of these subgroups [4] probably helps explain why the study of sclerosant injections has failed to yield evidence of efficacy. One subgroup likely to have been enrolled in considerable numbers probably represents back pain due to osteoarthritis of the lumbosacral facet joints, for which there would be little expectation of benefit from the materials used or the sites injected.
The other main subgroup likely to have been involved with what they called mechanical and/or instability is the rotation strain pattern, which may well overlap with the clinical features. If this were so, it seems that the injections might well have helped the problems at the lumbosacral level, where the injections were given, but not at the dorsolumbar junction, where there are almost invariably associated sites of impairment which refer pain downwards and often continue to cause the patient the sort of disability and handicap picked up on the disability questionnaires used in the study of Dechow et al. [1]. There would be little indication of improvement until the problems at both levels had been helped.
The subgroups can be identified from evidence collected in the clinic, such as side of back pain at rest, side of pain induced by side bending and rotation, and side and level of tenderness on palpation. It may well be that inclusion of such evidence in future studies will help reveal a lot of potentially useful hidden information.
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