10 The Scientific Basis of Leech Therapy

Mechanisms of Leeching and Their Clinical Correlatives

When a leech bites, the bite wound immediately begins to bleed and continues to bleed for several hours. This prolonged bleeding is due to the presence of hirudin and other anticoagulant substances in leech saliva and it is the most relevant mechanism of leeching in plastic and reconstructive surgery. Leeching achieves extensive local venous drainage and improves the hemorheological characteristics of the blood to effectively counteract post operative venous congestion and imminent tissue necrosis. Although the secretion of hirudin by the leech only represents a local tissue injection, systemic effects of hirudin are also presumed to occur. In a cohort of 23 patients, a reduction of viscoelasticity and aggregation tendency of the blood was observed four weeks after a single leech treatment in the lumbar region, while the hematocrit and plasma viscosity values remained unchanged [5]. Considering the short plasma half-life of hirudin, the authors proposed that differential stimulation of erythropoiesis might be responsible for the long-term modulation of hemorheological parameters. However, such systemic effects of leeching are of little importance in surgical indications for leech therapy.

Leeching is no longer recommended for prevention and treatment of thrombosis. Modern drugs such as heparin and coumarin have reliably effective and controllable pharmacological effects and are now preferred for these indications.

Analgesic and Anti-inflammatory Effects

A number of the known biochemicals in leech saliva exhibited analgesic and anti-inflammatory properties in experimental studies [2, 16, 17] (see Chapter 11 for more information on the biochemistry of leech saliva). Recent studies on hirudin and thrombin inhibitors have highlighted the direct anti-inflammatory effects of these substances in addition to their known anticoagulant effects. Experimental studies by researchers at the University of Lausanne have received much attention [10]. The investigators first produced antigen-induced joint inflammation in experimental animals and then treated the animals with subcutaneous doses of recombinant PEG hirudin for 13 days. Significant scintigraphic reduction of inflammation and histological reduction of synovial thickening occurred within seven days. These findings suggest that the inhibitory effect of hirudin acts not only on the thrombin system, but also on inflammatory processes at the cellular level. In another study, they showed that hirudin inhibits a number of proinflamma-tory cytokines in synovial fluid [22]. In leech therapy, it is important to bear in mind that a leech bite represents only a single hirudin “injection” and that the half-life of natural hirudin is shorter than that of recombinant PEG hirudin. As already mentioned, hirudin normally works in combination with many other anti-inflammatory substances in leech saliva. This additive effect is presumably very significant.

The jaws of the leech pierce the skin so that these potent biologically active substances can penetrate into the deeper tissues. Hyaluronidase (spreading factor), an enzyme in leech saliva, further facilitates the penetration and diffusion of these pharmacologically active substances into the tissues (see Chapter 11). Experimental research data on commonly used topical antiphlogistic drugs can be used to draw certain general conclusions about the accumulation of locally administered substances in body tissues. After topical application of diclofenac gel to the knees of patients with knee joint effusions, the drug could be detected in the deep periarticular tissues and body compartments [15]. With the additive effect of hyaluronidase, it is highly probable that the antiphlogistic substances in leech saliva can penetrate deep enough to exert significant effects on periarticular myofascial structures and perhaps even on intra-articular structures. A recent study showed that periarticular myofascial structures play an important role in the development of chronic joint pain and regional pain syndromes in patients with osteoarthritis [4]. A systemic anti-inflammatory effect of leech therapy is less plausible, especially in light of the prolonged effect of a single leech bite.

Segmental and Antinociceptive Effects

As a rule, any treatment that causes irritation of the cutis and subcutis will trigger local antinociceptive and segmental effects. This is the rationale behind the use of specific antinociceptive substances such as capsaicin (Spanish pepper) in pain treatment. These mechanisms are also involved in acupuncture and in the skin stimulation techniques employed in traditional European medicine (Braunscheidt’s technique, cupping, etc.). The extent to which a single leech bite activates such mechanisms is not known and is difficult to determine in experimental models. However, it would seem plausible that the antinociceptive effects of the leech bite might enhance the other primary mechanisms of leeching. The significance of segmental organization is often stressed in the historical literature. For example, one author states that leeches should be applied to the margins of the liver for treatment of hydropic liver congestion and to a defined connective tissue “headache zone” for treatment of migraines [3]. For the unbiased researcher, these theories can be interesting and merit further investigation. At present, the available study findings are insufficient to reliably determine whether there are clinical indications for leeching based on these mechanisms.

Effects on Lymph Flow and Connective Tissues

In addition to the aforementioned pharmacological effects, some investigators postulate that leeching improves lymph flow. The available data on this subject is sparse and stems from older studies [14]. Clinical experience with leech therapy in joint disease and pain management does not give any strong evidence in support of such an effect. There are no empirical reports of a specific effect of leech therapy on concomitant lymphedema. However, previous clinical studies have demonstrated the efficacy of leech therapy, even in patients without palpable tissue abnormalities or lymphedema. Likewise, some practitioners postulate that local leech therapy is especially effective in patients with so-called connective tissue zones. However, subanalyses of two large studies on leech therapy in the treatment of osteo-arthritis of the knee did not show any correlation between the extent of local connective tissue zones and the clinical efficacy of treatment [13]. Based on the current state of knowledge, the effects of leech therapy on lymph flow and connective tissues seem to be of little relevance to pain management, but the stimulation of lymph flow might be more important in the treatment of symptomatic varicosis. Further clinical studies are needed for a reliable assessment of such effects.

Traditional and Constitutional Concepts of Efficacy

In European, humoral, and Arabian medicine, as well as in Ayurveda and Traditional Chinese Medicine (TCM), leeching is closely associated with the constitutional theories and concepts of disease. In these systems of medicine, local and systemic states of surplus and deficit, heat and cold are considered when assessing the patient. All of these systems describe treatments invol ving local skin irritation and venesection as “drainage of surplus fluids.” It is theoretically possible yet methodologically difficult to analyze treatment responders according to these criteria. First of all, adequate standardization of the relevant terminology and clinical classifications is lacking. Secondly, responder analyses require a very large number of cases and a study design amenable to such an analysis. In our studies we were unable to demonstrate a correlation between the efficacy of leech therapy and initial hematocrit levels, the extent of blood extracted by the leech, or the body mass index (BMI), which were used as approximate parameters of constitution. However, no specific techniques of constitutional medicine (e. g., tongue diagnosis) were used to evaluate the patients. Therefore, it is not possible to rate the response to leech therapy based on traditional concepts of constitutional medicine at present. Even though the models underlying these traditional concepts now have a more metaphorical sense that does not comply with modern pathophysiological concepts and action principles, the fact that they served as the basis for proper and presumably successful leech treatment for centuries must be emphasized. Comprehensive scientific analyses of leech therapy should therefore take such aspects into consideration if possible.

Proof of Efficacy in Specific Clinical Indications

Leech therapy has been used to treat acute postoperative venous congestion since the 1960s. In this indication, leeching is now an internationally established modality that can be classified as a standard treatment method (see Chapter 7). A number of published case studies, case series, and uncontrolled studies demonstrate the efficacy of leech therapy in these patients [9, 19, 23]. Venous congestion and subsequent thrombosis are serious and feared complications of skin flap transplantation and limb reconstruction surgery. The successful use of leeches to treat postoperative venous congestion after plastic and reconstructive surgery was mentioned by Dieffenbach as early as 1827 [25]. The first comprehensive international publication on the subject was by Derganc and Zuravic, who described their results in a series of 20 patients in 1960 [6]. Objective proof of the improvement of blood flow was later provided by Doppler laser studies performed by Hayden [8].

Various animal experiments, some of which had a randomized study design, have convincingly demonstrated that leech therapy improves perfusion in transplanted skin regions and is superior to other treatment modalities used to restore normal blood supply and drainage. However, controlled cli nical studies are still lacking. The feasibility of performing randomized controlled trials is limited because it is hard to standardize the field of indication and the treatment procedure for postoperative venous congestion. Furthermore, the overall number of cases is very small. Because leeching is now an established form of treatment in this indication, it would seem ethically untenable to withhold the treatment from patients in the control group of a study. Consequently, it is very unlikely that such a study will ever be performed. The situation is similar to that of numerous surgical indi cations where a treatment form is viewed to be the standard treatment method even though the treatment lacks the high-level proof of efficacy defined by the criteria of evidence-based medicine. Numerous observation studies and case series on the use of leech therapy to treat acute venous congestion have been published in the international literature since 1960. In spite of the lack of controlled studies, one can therefore conclude that there is sufficient clinical proof of the efficacy of leech therapy for this indication.

Related posts:

Introduction Contraindications Safety and Adverse Effects of Leech Therapy Legal Aspects of Leech Therapy in the EU and USA Leech Therapy in Rheumatic Disease The Biochemistry of Leech Saliva

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