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Mechanisms of Leeching
The Technique of Leech Therapy
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By Brian Reid
Special to The Washington Post
Tuesday, November 4, 2003; Page HE01
Could voracious bloodsucking creatures, looking for a new post-Halloween role, find it in medicine? In a paper published today, a group of researchers suggests that letting four to six leeches suck away for an hour or so can dull the pain of osteoarthritis of the knee for weeks.
The work, done by a group of German doctors and published in the Annals of Internal Medicine, compared 24 patients who received one round of leech therapy -- just over an hour of sucking by four to six of the worms -- to 27 patients who received a single dose of a painkilling gel. A week after the treatments, the bloodletting group reported feeling significantly better than their undrained peers. Three months later, this difference was not statistically significant, though patients in both groups reported feeling better than before they started.
"Currently, no pharmacologic agent has similar lasting effects after a single, local administration," wrote the authors, from the academic teaching hospital of the University of Duisburg-Essen. While acknowledging that the mechanism by which leech feeding might relieve pain was unknown, they speculated that leech saliva may contain pain-fighting chemicals.
The idea that leeches could be used for pain control is not new -- medieval literature makes reference to the power of leeches to "salve . . . hurts." In modern medicine, though, it seems more incongruous for patients to offer themselves as supper to three-jawed parasites most often found at the muddy edges of freshwater lakes. Just a few inches long, the animals feed solely on the blood of mammals, sucking in several times their own body weight and living off the meal for months.
But medicine embraces many seemingly strange things, and some doctors whose patients come into regular contact with the creatures say there does seem to be a numbing effect to leech bites.
"I talk to a lot of fishermen," said Nadine Connor, the director of the division of otolaryngology at the University of Wisconsin-Madison. "If you talk to people who have had leeches on them when they were fishing, they'd say, 'I didn't even feel it.' There is, theoretically, an analgesic anesthetic, but that has not been isolated."
Still, experts warned that the nation's 20 million-plus people with osteoarthritis -- a degenerative joint disease with less than ideal treatment options -- shouldn't plan on making a run on leech vendors anytime soon. The study was small, and because leech treatment is so, well, distinctive, it is impossible to make the study a blind one. Every patient who received leech therapy knew it, unlike in most medication trials, where patients are left to wonder whether they received the active product or a placebo.
Further complicating things, the researchers found that patients who agreed to the leech therapy were more likely to anticipate success than those who received the gel.
"If you had osteoarthritis of the knee that was painful and someone gave you the opportunity to have leech therapy, you'd have to be willing to put leeches on your knee and you'd have to have some expectation of benefit," said Marc Hochberg, the head of the division of rheumatology and clinical immunology at the University of Maryland, who wrote an editorial accompanying the study.
Not only does the study design render the results less than compelling, wrote Hochberg; the lack of understanding of why leeches should work well in pain control also suggests the findings be viewed with caution. No one has yet isolated an ingredient of leech saliva that might be responsible for a painkilling effect.
And there are other drawbacks, ranging from common but harmless itching that affected most of the participants in the leech group to the potential for bacterial infections stemming from the fact that leeches can't exactly be sterilized.
In the editorial, Hochberg -- who has studied and recommended other nonconventional arthritis treatments such as acupuncture -- says he's not ready to start referring patients for leech therapy.
"This is not a therapy that should be mainstream," he said. "There's a lot people can do for OA if they don't want to take traditional medication."
Out for Blood
The uncertainty surrounding the use of leeches in arthritis contrasts with the way the creatures are used for surgical recovery across the world. Over the past two or three decades, the tiny bloodsuckers have become a common tool in microvascular surgery, a delicate procedure often used in major reconstructive surgery -- procedures in which parts of the body are rebuilt after injury, defect or disease -- or the reattachment of amputated body parts. Prior to this development, leeches' place in medicine was largely confined to medical history texts, which told how doctors since antiquity used the creatures to help balance the body's four "humours": blood, phlegm, black bile and yellow bile.
In microvascular surgery, blood circulation can be hampered when blood flows too quickly into still-healing veins, a complication known as a venous congestion. If the blood is allowed to pool, the new tissue may die. Enter the leech.
By sucking out blood, the leech relieves the pressure on the vein. At the same time, the affected area gets bathed in leech spit, a potent blend of anti-clotting chemicals that keeps blood moving. The most important component of the saliva, a chemical called hirudin, has been isolated, synthesized and approved by the Food and Drug Administration as an injectable treatment to fight a rare but dangerous reaction to the blood thinner heparin.
"We've used them very successfully," said Baylor College of Medicine plastic surgeon Jeffery Friedman, who admits that most patients express some shock at having days of leech therapy. But Friedman said the benefits are enough to win converts. "When they understand the consequences of not using them, they become very interested."
But the leech isn't the perfect tool, according to Wisconsin's Connor, in part because the worms don't follow instructions very well and have to be closely tended. As a result, even though leeches themselves are cheap, the medical personnel who help administer the therapy are not. And given that surgical patients often require continuous leeching for a week or more, we're talking hundreds of leeches.
"Leeches are not part of the team," Connor said. "They migrate. They disappear. They get lost in bedding. They get lost in orifices of the body. They're not reliable. They're not trying to save tissue -- they're trying to fill their gut with blood."
And the squeamishness factor isn't insignificant, either, Connor says. She is working with colleagues to create an "artificial leech," a device designed to have all the benefits of the creature without the mess and the unpleasantness. "There has to be a better way," she said.
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