Leech therapy rarely ever leads to serious complications. The local pain of treatment and short-term itching are regular side effects. Prior to treatment, the patient should be advised accordingly and asked to sign a consent form describing the relevant side effects (see Appendix). Prevalence data from systematic and prospective studies are only available for some of the different side effects of leech therapy. The following analysis was compiled using the data from published efficacy studies and case reports, as well as from personal observations. Quality control data on adverse events documented in more than 1000 cases treated at Essen-Mitte Hospital, mostly for treatment of degenerative joint disease, were also included in the analysis.
Local Pain During Treatment
Perceptions of the local pain of leeching vary. Most patients describe a local dragging pain that occurs immediately after the leech bites and persists for around one to five minutes. As more and more saliva is introduced into the tissues, the anesthetic effect of leech saliva begins to take effect. The intensity of the pain of the leech bite and the first phase of feeding is generally described as mild or negligible (depending on the individual’s pain threshold), but some patients find the pain more intense, similar to that of a wasp sting. The perceived intensity of the leech bite varies from one individual to another. Subjective pain ratings range from “hardly noticeable” to “mild” (similar to the pain of stinging nettle) to “similar to a wasp sting” (very rare). A slight (or sometimes somewhat stronger) rhythmic pulling sensation is usually noticed for the first one to three minutes after the start of feeding.
Whether stimuli of exactly the same intensity are perceived as painful or are not perceived at all is certainly dependent on the individual’s personality, but also depends on that person’s concentration on the leech or attitude toward leech therapy. The size of the individual leech’s jaw, the strength of the bite, the intensity of suction, and the volume and composition of the leech saliva also play a role. Many people never even notice the leech bite, for example when they are bitten under water while their attention is focused on something else. Frequently, the more anxiously the patient focuses on the leech preparing to bite, the higher the pain perception. The leech therapist should keep this in mind during the preparation phase and during treatment. A diversion can sometimes be helpful. It is also helpful to allow the patient to “get to know” “his” or “her” leech and to reassure the patient by handling the leech in a confident manner. If latex gloves must be worn for hygienic reasons, the leech therapist should never use forceps on the leech. Many patients lose their aversion to leeches when they are shown how elegantly they swim and the beautiful colored pattern on their back is pointed out. Many people report that the patient’s attitude toward the leeches changes from negative to positive after a positive treatment experience. Most of the apprehensions projected onto the leech are based on archaic fears rather than on objective facts. We also advise against killing leeches in front of the patients. If the leech is to be killed after treatment, the animal should be frozen and placed in a 90% alcohol solution a few days later.
Transient itching at the site of the leech bite in the first few days after treatment is very common and should not be mistaken for an allergic reaction. In the study of the efficacy of leech therapy in patients with osteoarthritis of the knee, roughly 70% of patients treated with leeches developed local itching that lasted a mean of two days. Transient itching occurs at a comparable frequency, but stronger intensity levels in many cases where leeches were applied to more peripheral joints, for example the thumb, but at lower levels after treatment of large joints and vertebrogenic zones, according to empirical assessments. The patient could be advised of these side effects prior to treatment. The patient should never scratch the leech bite, especially after initial wound closure, because this frequently delays wound healing. We recommend local cooling remedies (curd wraps, cold moist wraps, vinegar wraps). For more severe itching, commercial antipruritic products (e.g., Fenistil ointment) or oral antihistamines may be used. Some leech therapists prescribe concurrent oral antihistamines for patients with a known history of severe reactions (itching and skin reddening) to leech therapy. Isolated reports describe brief recurrences of moderate itching in certain situations (e.g., high temperatures) over the course of several months after an otherwise uneventful course of leech therapy.
Hypotension and Vasovagal Attacks
Patients with a history of developing vasovagal attacks or syncope (fainting) before other invasive treatment methods may also develop such a reaction at the start of or during leech therapy. One survey showed that vasovagal attack occurred in one out of 1000 leech treatments performed at our hospital. Therefore, the leech therapist should always ask about the patient’s prior history of vasovagal attack or fainting before procedures such as blood sample collection or acupuncture. To guard against vasovagal attack, the patient should drink plenty of fluids before and during treatment, and treatment should always be performed in a calming environment while the patient is lying down. Two outpatient cases of hypotension and vasodepressor syncope following leech therapy were also observed. Both patients had known arterial hypertension and were on triple antihypertensive medication, which they continued taking as usual. A few hours after leech therapy, both patients developed a brief attack of benign syncope. It is important to remember that leeching has a known antihypertensive effect when treating patients on antihypertensive medications. Patients should drink plenty of fluids. If there is a strong flow of blood from the leech bite, the patient’s blood pressure should be monitored and antihypertensive medications should be adjusted as needed.
Leech therapy is always associated with a certain degree of blood loss, which is clinically irrelevant in most cases. In the clinical trial by Michalsen, the mean hemoglobin loss was 0.7 mg/dL, and clinically relevant blood loss did not occur in any of the patients studied. However, there have been isolated observations of stronger afterbleeding with a corresponding decrease in hemoglobin, particularly in cases where a leech was inadvertently applied directly to a superficial vein. According to the records of Essen-Mitte Hospital, a clinically relevant decrease in hemoglobin (> 3 mg/dL) occurred after leech therapy in two patients, one of whom required a blood transfusion (after being treated with six leeches for osteoarthritis of the knee). Asked retrospectively, one of the patients stated that she had, in her opinion, experienced prolonged wound bleeding in the past. In another case, afterbleeding from the leech bite lasted over 36 hours and had to be stopped with a cutaneous suture. Extensive coagulation tests were then performed but did not reveal any specific coagulation disorder. Prior occurrences of abnormal bleeding seem to be anamnestically important, and patients should be specifically asked about such events. Anticoagulants are important concurrent medications to watch for. If low-dose aspirin is prescribed in combination with other platelet aggregation inhibitors (clopidogrel, Iscover, Plavix) or high-dose fish oil (Omacor), a smaller number of leeches (three to four) should initially be used. Blood counts should always be obtained before starting leech therapy. To reliably prevent the loss of relevant quantities of blood, the leech therapist should never use more than 12 leeches in a single treatment session.
Impaired Wound Healing, Superinfection, and Allergies
After the leech drops off, the edges of the three-pronged wound generally swell for 12-48 hours accompanied by a feeling of local tension, heat, and reddening. Small blood spots (ecchymoses) develop below the skin around the leech bite. Larger collections of blood rarely develop. As with superficial bruising, the blood spots are initially reddish violet, then turn yellowish, and finally disappear within around two weeks. Localized inflammation, sometimes with papulous elevation of the bite sites, is a relatively common problem that is often accompanied by itching . These inflammations usually subside quickly when iced and left undisturbed. The cause of this wound-healing disorder is unknown. Improper handling, especially early stoppage of afterbleeding from the wound, squeezing the head of the leech with forceps, forceful removal of the leech before it has finished feeding, and failure to keep the animals in fresh water, have frequently been implicated as potential causes. However, this has also been observed to occur after proper leech handling in isolated cases. Theoretically, local infection with Aeromonas hydrophila is a potential cause, but there has been no microbiological evidence so far of the presence of Aeromonas hydrophila in the wound secretions from the affected patients. More severe local inflammations are most commonly caused by secondary wound contamination or irritation due to mechanical irritation, such as scratching and rubbing. The patient should be thoroughly advised of the importance of protecting the wound from mechanical irritation. According to the hospital survey, more severe localized inflammations occurred in three isolated cases: One patient developed erysipelas and two developed moderate lymphangitis. All cases resolved quickly in response to antibiotic treatment with cephalosporins and/or gyrase inhibitors. Strict adherence to contraindications and localization recommendations minimizes the risk of localized inflammation. In unclear cases where progressive and painful skin reddening develops, especially if associated with increased temperature, the leech therapist should know to administer antibiotics immediately. Pseudolymphomas may occur in rare cases; these papulous efflorescences are caused by an arthropod reaction to the leech bite. Currently, there is no data by which to assess the precise frequency of this adverse effect. To our knowledge, a total of three documented and confirmed cases have been reported.
It is difficult to distinguish secondary wound-healing disorders from potential allergic reactions. Precise data on the frequency of allergic reactions to leech bites are not available. Local itching, a common side effect of leeching, should not be interpreted as an allergic reaction. Unequivocal allergic reactions such as transient urticaria and locodistant swelling have been reported in a few isolated cases. However, localized symptoms, reflex erythema, and urticarial dermographism in psychovegetatively labile individuals have been observed more often. An older case report describes the occurrence of a short-term anaphylactic shock after application of six leeches to the temple region. Some leech therapists administer systemic antihistamines for treatment of local allergic reactions with (empirically) good success. However, the good response rate to antihistamines is not proof per se of an allergic cause: A certain rate of placebo response to antihistamines must also be taken into account. The possible boosting of an existing antibiotic allergy by leech therapy was also proposed in a case report.
When interpreting local reactions that occur following leech therapy, it is important to remember that the proteases in leech saliva release various types of nonimmunological mediators. Furthermore, such reactions can be aggravated by psychovegetative factors. All in all, there are only a few cases in which an association between leech therapy and the occurrence of allergic reactions has been proved with sufficient certainty. However, allergic reactions may potentially occur after exposure to any foreign proteins. Contact dermatitis has also been observed after use of leech ointment.
Short-term reactive swelling and/or tenderness of proximal lymph nodes has occasionally been reported, but most commonly in patients with delayed wound healing. These symptoms have most frequently developed in the groin region after application of leeches for treatment of the knee joint, hip joint, or varicose veins. Rapid and uneventful disappearance of lymph node swelling is described in all of the case reports.
Sepsis due to systemic infection with Aeromonas hydrophila has been repeatedly observed after leech application in reconstructive surgery indications, but not in any of the other relevant fields of use. This supports the conclusion that the risk of Aeromonas hydrophila sepsis is increased only in patients with severe underlying diseases or immunosuppression, which is often the case in surgical candidates for leech therapy. We therefore recommend concurrent antibiotic treatment for all surgical patients receiving leech therapy . In the remaining fields of use, primary antibiotic therapy does not appear to be necessary according to the current state of knowledge, but relevant contraindications must be observed.
Transmission of Infectious Diseases
Today, medicinal leeches are generally only used once. Therefore, there is no risk of the indirect transfer of infectious diseases from one patient to another. Primary infection with Aeromonas hydrophila is clinically relevant only when leeches are applied to surgical transplants. Concurrent antibiotic treatment is therefore recommended for infection prophylaxis in these cases (see above). The transmission of other bacterial or viral pathogens to humans within the context of leech therapy has not been observed so far.
When left undisturbed, leech scars usually quickly shrink to hardly visible or invisible tiny three-pronged marks that disappear completely within one to three weeks. However, if wound healing is impaired due to scratching or secondary wound infection, the scars may remain visible for significantly longer periods of time. Papulous skin changes persisting for several months have also been reported in isolated cases. In one case, a permanent “arthropod reaction” was also reported to occur after leech treatment. Significant scarring may occur particularly when leeches are applied to
areas with thin skin and thin layers of subcutaneous tissue or joint regions where the skin is in constant motion. The wearing of restrictive clothing after treatment, for example around the knees, can also result in scar formation.
For esthetic reasons, restraint is advised when using leeches in the facial region or in other clearly visible and cosmetically relevant parts of the body. Here, we again stress that it is necessary to thoroughly inform the patient about the potential risks of treatment, including scarring, and to obtain written informed consent from the patient before going ahead with the treatment.