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Zit bacteria causing back pain - a spotty hypothesis

You are most definitely going to hear a lot more about this Danish study regarding back pain. The claim the researchers are making is very interesting. They present plausible preliminary evidence that a bacteria called Proprionibacterium acne seems to be present in some degenerated lumbar discs at rates well above chance. This is the same bug which is thought to cause good old spots, zits, blinders etc (the clue is in the name). They also report that a prolonged course of a common antibiotic (100 days was the duration chosen, rather arbitrarily perhaps) was able to significantly reduce back pain symptoms in patients with a particular type of MRI change on their scans.

These studies have been greeted with fairly fulsome praise from some quarters and more measured reporting from others. There has been talk of Nobel prizes. I wouldn’t disagree that if firmly established this could be the biggest advance in infectious diseases since Barry Marshall chugged a schooner of live Helicobacter Pylori on stage at a conference to highlight his and Robin Warren’s work on its link to gastric ulcers. Not many voices are being raised in reply.

Here are my comments about this work in no particular order

-The proposed mechanism is plausible, though there are some significant issues. P Acnes is a very low-virulence organism and its presence may well be incidental or an epiphenomenon. It can provoke inflammation with even a low-grade infection however, and this is perhaps the main appeal of the hypothesis.

-Establishing a causal relationship for an organism to cause disease is usually done by proving Koch’s postulates for the bug concerned. This hasn’t been done for P Acnes in LBP.

-Another reliable set of criteria for establishing causation is the Bradford Hill criteria, which is also far from being completed. More basic science will surely follow as a matter of urgency now this evidence has been published. Note that Marshall and Warren had mostly done all this groundwork by the time they advanced their hypothesis to public attention.

-The antibiotic used in the study was Amoxycillin combined with Clavulanic Acid. Clavulanic acid has been previously shown to have an anti-inflammatory action via its ability to inhibit pro-inflammatory cytokines. In other words, a large and well-established body of research suggests that the antibacterial action of the antibiotic may very well be irrelevant to its painkilling ability. I have several patients with chronic pain of various types whose pain is temporarily relieved for a few weeks by a stiff course of antibiotics.

-Extraordinary claims demand extraordinary evidence. The evidence presented by these researchers is fascinating and intriguing but most definitely not extraordinary. As well-conducted as this research has been, the idea that ‘40% of all chronic back pain can be cured’ is completely misleading and overblown. In fact, the research as presented does not in fact suggest a cure but just a reduction in average levels of pain.

-Even if one accepts the slightly patchy argument that a substantial chunk of chronic back pain is due to infection by P Acnes the proposed treatment is highly problematic. Overuse of Amoxycillin/Clavulanic acid is one of the major contributing factors to the rise of antibiotic-resistant superbugs. A prolonged course as described would leave you with nothing but a gutful of highly antibiotic-resistant flora. Serious superinfections from notorious marauders such as Clostridium Difficile would be inevitable. Such superinfections take weeks of isolation and barrier nursing to resolve. Not to mention the routine diarrhoea. You may well not fancy the idea of needing a faecal transplant to cure a life-threatening complication of your back pain treatment.

-There is no really practical way to tell yet whether any given individual would benefit from undertaking a trial of such experimental therapy. Chronic pain sufferers are incredibly easy to sign up for improbable treatments, and their interests need to be advocated for by subjecting any claim to a cure to serious scrutiny. I wouldn’t recommend this therapy to one of my patients unless I had a way of knowing I could offer them good odds.

So hold the phone to Stockholm. Proposed mechanisms of causation for chronic back pain have come and gone. This one is at least plausible, and gives a direction for further research. In the best tradtions of science, it allows one to formulate disprovable predictions. Although regular careful readers will be abl to detect the undertone of optimism and excitement in my appraisal, this proposed mechanism of long-term back pain has a long way to go before I’m going to call it revolutionary.

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