maggots & wound healing – some truth in folk wisdom?

Blogging on Peer-Reviewed Research One of the things that distinguishes medical science from what is often called ‘complementary & alternative medicine’ (aka CAM) is the willingness of the former to carry out careful, well-designed tests of various therapies. Those treatments shown to have some therapeutic value are added to the tools available to doctors & surgeons; those which don’t, aren’t. 

Over the years, a number of therapies that might once have been seen more as folk medicine have entered the mainstream. One of these is the use of leeches: once the tool of ‘barber-surgeons’ at a time when one of the main treatments for just about anything was to bleed the patient, leeches are now part of mainstream medical practice. (Frankly, if I’d lived back then & couldn’t avoid a good bleeding, I’d have much preferred the leeches to the barber-surgeon’s non-sterile knife! Although I suspect you could still pick up a bacterial or viral infection acquired up by the leech from the last person it sucked on.) They can be used after surgery to reattach skin and underlying tissues, to enhance blood flow to the affected area until veins have regrown.

More recently the use of maggots has become reasonably common as a tool for clearing dead (necrotic) tissue from in & around open wounds. Maggots are fly larvae; the ones used in wound treatment are typically blowfly larvae. But there’s no danger of them gorging endlessly on the patient’s flesh as they really only go for dead tissue. However, despite their increasing popularity, there hasn’t been much in the way of a clinical trial of maggots & wound healing (if you have a weak stomach there are some high-ick-factor images here; they lack a good explanation but essentially show the progression of an ulcer under maggot treatment). That is, until the one described in a just-published paper in the British Medical Journal.

This clinical trial (Dumville et al., 2009) compared the effectiveness of maggot-mediated wound healing with the ‘standard’  (hydrogel) treatment. While the one previously published study compared the two treatments in terms of their ability to debride a wound (i.e. remove dead tissue), Dumville’s team was interested in how well the treatments promoted healing. They were also interested in whether the treatments differed in terms of time to debride necrotic flesh, effects on bacterial load in general & presence of MRSA (the ‘superbug’, methicillin-resistant Staphylococcus aureus), adverse events, & ulcer-related pain. To put their study in context, the authors comment that larvae are increasingly used to treat leg ulcers and are thought to stimulate healing, reduce bacterial load, and eradicate MRSA. Clinical evidence to support larval therapy comes from a small randomised controlled trial that did not follow patients to healing.

The trial involved 267 patients, all of whom  had at least one venous leg ulcer with a significant area of dead tissue in & around it. While this isn’t a huge number of patients, the authors point out that it was actually rather difficult to enrol people in the trial, not least because there weren’t all that many people presenting with the ‘right’ type of ulcer. There were three treatments: the standard debridement treatment of a compound called hydrogel, along with compression bandaging; ‘bagged’ larvae ie maggots in a mesh bag, so they couldn’t move around the wound to any great extent; & ‘free’ larvae (which speaks for itself!).

You may well have realised that this protocol means that the trial wasn’t blinded – the patients knew which treatment they were getting, and that this could have had an impact on their perceptions of how the treatment affected them (things like pain, or feelings of overall wellbeing). And indeed, this may possibly have happened. Certainly, one of the study’s findings was that ‘maggot-treatment’ patients reported higher levels of pain associated with the 24 hour period before the first round of maggots were removed from the wound. Howver, it’s difficult to imagine how this particular trial could have been blinded – apparently you can’t use compression bandages with the maggots (squashed larvae, presumably), so it would be easy to tell which treatment you were getting.

What else did the team discover? Well both maggot treatments cleaned out dead tissue faster than the standard hydrogel therapy. (My understanding is that this relies on gunky dead bits coming off with the dressing when it’s removed – ouch!) So if you want a wound cleaned out quickly, perhaps in advance of a skin graft, then maybe maggots would be the way to go. But – there was no significant difference between treatments in terms of time to wound healing, or of bacterial load. As for MRSA, only 18 patients presented with an MRSA infection, but again there seemed to be no signfiicant difference between the treatments as far as clearing the infection went.

There’s a lot more research to be done in this area before doctors consider throwing out the hydrogel & buying in quantities of maggots. (And, I suspect, a fair bit of patient education – not eveyone would be delighted at the prospect of blowfly larvae crawling around in a wound.) For example, it’s not clear from this initial study that faster removal of dead tissue has any effect on overall speed of wound healing. The team concluded that [research] is needed to explore the relation between debridement, healing, and microbiology as well to better understand the value of debridement as an outcome from the patient’s perspective.

J.C.Dumville, G.Worthy, M.Bland, N.Cullum, C.Dowson, C.Iglesias, J.L.Mitchell, E.A.Nelson, M.O.Soares & D.J.Torgerson (2009) Larval therapy for leg ulcers (VenUSII): randomised controlled trial. British Medical JournalBMJ 2009; 338:b773 doi:10.1136/bmj.b773

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