Convenient culprit: Myths surround the brown recluse spider
■ The reputation of the shy, retiring Loxosceles reclusa far exceeds the spider's range, confusing efforts to diagnose or accurately track the true incidence of its bite.
By Nina Sandlin — Posted Aug. 5, 2002
Last fall, when a 7-month-old child, admitted to a New York hospital with a swollen arm and a runny sore, developed hemolytic anemia, the working diagnosis was brown recluse spider bite.
But days later, cutaneous anthrax was reported at media offices in the city, and the baby, who had visited the ABC News studio with his mother, tested positive for the bacilli. The infant's severe systemic symptoms were atypical for anthrax, a disease all but unheard of in U.S. population centers for decades.
It was, in other words, an interesting case, and one that drew significant attention in light of the national emergency -- the country's youngest anthrax victim. But in other respects, the case was commonplace.
More than 2,000 brown recluse bites are reported to poison control centers each year. And, if epidemiology and confirmed cases are any indication, most of them are something else.
"Doctors are horrible [about] misdiagnosing any kind of necrotic-looking wounds as brown recluse bites," says Sean P. Bush, MD, a professor of emergency medicine at Loma Linda School of Medicine. An envenomation specialist, he has become the "go-to doctor" in Southern California for suspected spider bites.
In the emergency department "you see a necrotic wound every other shift," he says, but spider bites are a rarity. Even with black widows, which "are totally ubiquitous here," he only sees about half a dozen bites a year. "If it's an 'exciting year,' maybe 10."
And Dr. Bush doesn't see any brown recluse bites.
"There are no populations of brown recluses in California," wrote Richard S. Vetter in the Western Journal of Medicine in November 2000, yet "several hundred cases of 'brown recluse bites' have been reported to me in the past decade."
"The medical community believes the brown recluse is a common constituent of the spider fauna throughout the country," says Vetter, an arachnologist at the University of California, Riverside. He and Dr. Bush co-authored the Annals of Emergency Medicine's May editorial on overdiagnosis of brown recluse bite.
They're not the first to try to correct that impression. In 1983, arachnologist Willis Gertsch, PhD, and toxicologist Findlay Russell, MD, wrote in Toxicon that of some 600 spider bite cases seen at Los Angeles County General Hospital over 10 years, 80% were something else. "Patients came to the hospital as ... 'probably brown recluse,' and the brown recluse is not found within a thousand miles of the hospital," they wrote.
Facts and fictions
The brown recluse, Loxosceles reclusa, inhabits primarily South Central states, from Texas to Tennessee. But bites are reported regularly across the country.
It is a myth, says Vetter, that brown recluses are transported all around the country and "that's how people get bit."
Isolated itinerant individuals could not be responsible for the hundreds of bites reported outside the spider's territorial range every year. Populations of related Loxosceles species exist in Southwest deserts, but virtually all bites are reported from populated areas.
Even in places thick with spiders, real bites are rare.
The shy, retiring recluse is seldom encountered, if it can avoid it. Nocturnal, fragile and easily damaged, it bites when crushed in its retreat, or when someone rolls onto it in a bed it has unwisely started across.
Often the victim is initially unaware of the bite. In part, this reflects a fact of spider biology. Arthropods such as bees use their venom defensively, and it has evolved to induce pain. But spider venom is used to immobilize prey. Creating pain in mammals is an irrelevance.
Few spiders are poisonous to large animals; most cannot even pierce human skin. Of the spiders that can bite people, most are merely a nuisance. But spider venom is remarkably diverse. Several varieties are capable of causing mildly necrotic wounds, referred to as necrotic arachnidism.
The venom of Loxosceles species contains sphingomyelinase D, a wholly unique venom component in the animal kingdom, says Hernan F. Gomez, MD, a University of Michigan researcher in spider bite toxinology. He and his colleagues have developed an immunoassay capable of detecting Loxosceles venom for up to a week after envenomation.
Here's what often happens: People experience pain or tenderness several hours after the bite as SMD starts to trigger tissue damage. This can last up to six months. Most bites are uneventful. A minority develop the dermonecrosis that has made the spider famous.
In these cases, a bluish sinking patch with ragged edges and a surrounding redness appears within 24 to 72 hours, says William V. Stoecker, MD. He described clinical aspects at an arachnidism symposium that Vetter organized as part of June's American Arachnological Society meeting. This is the "red, white and blue sign." Bruising may spread along lymphatics, or with gravity. Often there is a central blister.
But these symptoms overlap with many other dermatologic conditions.
"I don't think it's easy just from the wound itself to say it is brown recluse," especially in nonendemic areas where one would seldom encounter it, said Kevin C. Osterhoudt, MD, a toxicologist at Children's Hospital of Philadelphia.
"Many physicians, when they see a necrotic wound, don't have a broad differential diagnosis for it. And they've been told that brown recluse is what causes wounds like that." At a recent conference of Pennsylvania emergency physicians, he asked how many had seen brown recluse in their ED "and most of them raised their hands."
Show me the spider
Media attention and public dread have made loxoscelism what Dr. Stoecker calls a "disease du jour," and many patients are convinced they have it.
"They get very angry and upset" if contradicted, says Dr. Osterhoudt. Many Web sites, he adds, tell of patients' "recurrent diseases brought on by brown recluse," and how "doctors just won't believe them."
This is exacerbated by poison control data, as centers are dependent on the information provided by callers.
Few patients present with a spider, though. Even a stomped-on specimen has diagnostic value, since specialists rely on the sclerotized genitalia, eye arrangement, and hard-to-squish features like leg spination (absent in Loxosceles), not the highly variable markings, to make their ID.
The paucity of authoritatively confirmed cases has plagued the literature. Researchers have had to use tiny samples and/or rely on presumed or probable cases. This leaves clinicians with a composite picture drawn in part from erroneous best guesses.
With no readily available test, most diagnoses -- and misdiagnoses -- are based on the general look of the wound.
"The most common thing I see misdiagnosed is just a common cellulitis," says Dr. Bush. "In the center of the wound there will be a little necrosis."
Dr. Stoecker, a dermatologist at the University of Missouri Health Sciences Center in Columbia -- the heart of brown recluse country -- offers some rules of thumb: "If you have a big bite, not irregular, no spread -- forget it."
That is more likely a bacterial infection, he says; or pyoderma gangrenosum: "It's big, it's wet. These things ulcerate early. Within three days, you can put a probe 10 cm into the wound." The lesion from a brown recluse bite is usually dry and not as extensive.
Dr. Osterhoudt in the May Annals of Emergency Medicine describes Lyme disease mimicking loxoscelism.
With rare conditions, misdiagnosis is even more of a danger.
For loxoscelism, supportive care is the standard. But many look-alike conditions call for specific treatments: antibiotics for bacterial infections; iodides for sporotrichosis; change of regimen for drug-related outbreaks. False spider bite diagnoses can delay or prevent treatment of serious conditions.
A worst case may be necrotizing fasciitis. "This is a medical and surgical emergency," says Dr. Bush. "You start broad-spectrum antibiotics immediately, and excision. You have to get out in front of it. NF has a huge mortality."
The systemic effects of loxoscelism, such as the hemolysis that complicated the New York anthrax case, are less common and poorly understood. They account for all eight recorded fatalities, most in children. In no case was the bite confirmed. There is no direct relationship with the severity of the wound.
Similarly, the hobo spider, Tegenaria agrestis, sprang to prominence with the 1996 publication of three dramatic cases, including a hemolytic fatality without a confirmed spider bite. Researchers have not yet reproduced the dermonecrosis attributed to the hobo, whose venom chemistry is not as well-known.
Data based on conjectural results have also made it hard to determine efficacy of various treatments. Among them: Dapsone, a sulfone antibiotic used to treat Hansen's disease, to damp neutrophil aggregation; hyberbaric oxygen to alter the venom's chemistry; steroids; electric shock and nitroglycerin patches.
Controlled studies have not yet found any therapy to be effective, although Dr. Stoecker suggests Lidoderm patches for pain. Surgical excision, once standard, is now thought to retard wound healing and to boost the release of serum amyloid protein, augmenting necrosis.
In Dr. Gomez's lab, however, a Loxosceles-specific antivenin inhibits the necrotic process in rabbits. Similar to CroFab, the rattlesnake antivenin introduced last year, the experimental antidote uses Fab fragment -- the antigen-binding portion of the antibody -- to inactivate the SMD and minimize the chance of an immune reaction.
Ironically perhaps, notes Dr. Gomez, it is the limited scope of the brown recluse -- that only "maybe 10 of the 50 states" have the spider and "the vast majority [of victims] will do just fine with purely supportive care" -- that makes it unlikely pharmaceutical firms will invest in bringing the antidote to market.
The "pharmacoeconomic obstacles" may not limit his lab's immunoassay, which would not require the same elaborate testing. And indeed, once optimized, it could play a key role in testing an antidote or other proposed treatments, by identifying confirmed cases.
Confirmed cases would change the brown recluse picture, Dr. Gomez says, making evidence-based medicine possible, and dispelling myth -- "because right now, in practical terms, there is no way to identify brown recluse bites."