Adverse Effects of Leech Therapy

Leech therapy rarely ever leads to serious complications. The local pain of treatment and short-term itching are regular side effects. 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" (sim-ilar 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.

Local Itching

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 described in Chapter 10 (p. 121), 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 an-tihistamines 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 re-currences 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 attacl<, 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.

Andreas Michalsen, MD, Department of Internal Medicine V, Germany