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Old 03-08-2014, 01:14 PM
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Default More Evidence: Microbial Infection Causal Factor

Bugs in the Back: Is Lumbago an Infectious Disease?
Paul G. Auwaerter, MDDisclosures
February 28, 2014

I just had my first consultation with a patient who came to the ID clinic asking whether Propionibacterium acnes was responsible for his chronic back pain. This is a man who has had multiple back surgeries and many previous interventions and treatments for his pain. He recently had been encouraged by family members, who had been trolling the Internet literature, to find out whether a chronic infection could be causing his back pain.

P acnes is often dismissed as a contaminant, but during the past decade or so it has been recognized as an indolent pathogen that can cause problems such as ventriculoatrial shunt infection and perhaps prosthetic joint problems, especially in the shoulder. In addition, a small amount of supportive literature about P acnes infection in the spine has been published. This infection often is not typical; patients have no fever or elevated sedimentation rate. It seems to be fairly rare; however, one review[1] found that 97% of 29 patients with this infection had previously undergone surgery.

Perhaps beginning with a report in the early 2000s in The Lancet, [2] some have speculated that P acnes may explain more mundane lower back pain or sciatica or problems attributed to a herniated disk, for example. A number of studies have supported[3-5] or refuted[6,7] this idea that an infectious cause may be responsible for some back ailments. A few of the studies purport to have used very careful techniques for removing disks and growing this anaerobic organism in cultures.

Recently, a group in Denmark has investigated this more thoroughly and published 2 papers of interest on the subject.[5,8] In the first,[5] they removed disks in 61 patients; P acnes was cultivated from 46% of these herniated disks, and 80% of those had specific MRI findings called Modic 1 (bone edema adjacent to the disk area). There are 3 different kinds of Modic descriptions, named after the physician who described them. Modic 1 means that the disk has caused some adjacent bony trabecular problems with microfractures and resulting serum leaking into the area, which leads to radiographic changes. Thus, perhaps a certain subset of back pain could be attributed to this.

But the proof would have to come, in my mind, from repeated cultures that recover this organism from not just one but multiple areas or perhaps a therapeutic trial. Indeed, the same group has published a therapeutic trial[8] in which patients with Modic 1 MRI findings were randomly assigned to receive either amoxicillin/clavulanate or placebo. Of 162 patients enrolled, 144 completed the trial and were available for follow-up. They all had at least 6 months of chronic low back pain and Modic 1 changes. Patients were randomly assigned to receive amoxicillin/clavulanate or placebo 3 times daily for 100 days.

At 1-year follow-up, there was a statistically significant difference between the antibiotic and placebo groups, with reductions in pain in the active treatment group that seemed to continue even after antibiotic cessation. In addition, the antibiotic group had more resolution of the Modic 1 changes.

These findings are intriguing. This type of antibiotic trial bears repeating in a different setting, and if it holds up, it is highly suggestive that a subset of patients with chronic low back pain may benefit more from antibiotic treatment than injections, neurosurgical interventions, and so on.

I believe this issue deserves close observation and may even be at the point where a trial of amoxicillin/clavulanate could be worthwhile in patients with back pain and Modic 1 changes. I will say that most P acnes isolates are susceptible to amoxicillin alone, which might be a better tolerated regimen, and perhaps the dose could be pushed a bit higher to 1000 mg 3 times daily.

Stay tuned because this particular area of study may change a certain subset of medicine. Whether we can go by MRI findings to make treatment decisions or need some kind of microbiologic confirmation is uncertain. There is biologic plausibility; the spinal column has unique characteristics that make the environment favorable for this particular organism.

Thanks very much for listening.

http://www.medscape.com/viewarticle/820717
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