Figure 2: The full-grown maggots are removed after three days of treatment. There is no necrosis left. The wound was treated with four applications with a total of 145 maggots. The wound was subsequently treated with vacuum-assisted closure therapy and secondarily closed.
Indications and Evidence
Indications and contra-indications for maggot therapy are not well defined. Some state that all kind of wounds that contain necrosis or slough can be good candidates for MDT. In our own study of 101 patients with 116 wounds treated with maggots, we had an overall success rate of 67%. (Seventy-eight out of 116 wounds had a beneficial outcome.) However, in 13 patients with septic arthritis, all wounds failed. Success rates where significantly reduced in cases of chronic limb ischemia, visible tendon or bone, and in cases of duration longer than three months before the start of MDT.11
Most physicians who start MDT use it mainly for worst-case scenarios. From our previous studies, it is clear that success rates in those patients are low. After witnessing a few failures, the physician is naturally reluctant to use it again.
What about evidence? Large randomized studies are lacking, although one containing 600 venous ulcer patients was initiated in 2004.12 There have been three randomized studies performed. Wayman, et al., have shown the cost-effectiveness of larval therapy in venous ulcers compared with hydrogel dressing.13 Contreras, et al., could not find a difference between MDT and curettage and topical silver sulfadiazine in patients with venous leg ulcers.14 At the 36th annual meeting of the European Association for the Study of Diabetes, Markevich, et al., reported on a randomized, multicenter, double-blind controlled clinical trial (n=140) for neuropathic diabetic foot lesions compared to conventional treatment. They found a significant higher percentage of granulation tissue after 10 days, compared with the hydrogel group.15 Results from large case-series indicate that MDT works and could even save limbs.2,16-18 The mechanism of action has not been unraveled yet.
Figure 3: A patient with a necrotizing fasciitis of the left upper leg is treated with the contained technique. There is no normal proximal skin border, which would be needed for the free-range technique.
Factors Influencing Effectiveness of MDT
Unfortunately, the statement made by Thomas, who said that maggot therapy works by “secreting proteolytic enzymes that break down dead tissue, turning it into a soup, which they then ingest,” still holds.19 It is known that there are mechanical effects, tissue growth effects, that direct killing of bacteria in the alimentary tract of the maggot takes place, and that maggots produce antibacterial factors.2,17,20-31
Although maggots are suitable agents for chronic wound treatment, it is likely that some wounds are more eligible than others for this type of treatment. In our opinion, all wounds that contain gangrenous or necrotic tissue with infection seem to be suited for MDT.32 Success rates of MDT reported in literature vary, but seem to be around 80% to 90%.16,17,33 In our own series, success rate is about 70%.
Patient-selection (case-mix) and method of outcome measurement play essential roles in these percentages. In our opinion, all wounds that contain necrotic tissue can be debrided effectively with MDT. However, if for example wound ischemia is the major etiologic factor, this should also be addressed. In our experience, diabetic foot, venous ulcers, traumatic ulcers, and infections after surgical procedures are all good candidates for MDT.
Absolute contraindications in our opinion are wounds close to large, uncovered blood vessels and wounds that need immediate surgical debridement (e.g., in the case of a septic patient). A relative contraindication is patients with natural of medically induced coagulopathies, but also patient preference could play a role.34 We have had very bad results with infected small joints of the foot; all wounds (n=13) eventually needed a small or large amputation.