Strategies to make a definitive diagnosis of osteomyelitis
Experts give tips to interpret imaging tests and create a tailored antimicrobial approach so you can prevent the condition from returning by Edward Doyle
Published in the July 2005 issue of Today's Hospitalist.
The elderly patient presents with a foot ulcer that may be infected. Because the patient, a diabetic, is neuropathic, she isn’t sure how long she has had the ulcer, and test results and lab values don’t provide a lot of information.
The patient’s sedimentation rate is just above 100, and her white blood cell count is slightly elevated. Suspecting osteomyelitis, you try to probe the bone, but the results are unclear. An X-ray of the foot produces similarly equivocal results.
If you’re not sure what to do next, you’re not alone. Diagnosing and managing osteomyelitis, particularly in elderly diabetic patients, can be difficult. Practice guidelines released last fall by the Infectious Diseases Society of America (IDSA), for example, note that osteomyelitis is the most “difficult and controversial aspect in the management of diabetic foot infections.”
When osteomyelitis is severe enough—you can probe bone, for example—you know that osteomyelitis is likely. But what about the less certain cases that you see on a regular basis in which the evidence is not clear?
Today’s Hospitalist talked to four different specialists—a hospitalist, an infectious disease physician, an orthopedic infectious disease physician and a podiatrist—to get some insight on how to diagnose and treat osteomyelitis.
1. Check your patients’ feet. While this may seem like obvious advice, experts say that too many physicians ignore their diabetic patients’ feet. But checking hospitalized patients for decubitus ulcers is an important step in detecting osteomyelitis before it produces serious damage. Lakshmi K. Halasyamani, MD, a hospitalist and associate chair of the department of medicine at St. Joseph Mercy Hospital in Ann Arbor, Mich., says that in a busy inpatient setting, the simple act of inspection often falls by the wayside.
“I can’t tell you the number of patients who come up to the floor and no one has taken their shoes or socks off to look at their feet or lifted up their gown,” says Dr. Halasyamani, who will talk about skin and soft tissue infections at the upcoming Fall 2005 Hospitalist CME Series. (For more information, see the special advertising section in this issue or go online.)
Gunner Deery, MD, an infectious disease specialist who co-authored the IDSA guidelines, says that time is often of the essence in catching foot infections. He warns that because elderly diabetic patients who are neuropathic can develop foot ulcers very quickly, even within 24 hours, hospitalists should examine their patients’ feet for ulcers daily.
“The feet often seem to be viewed as a secondary appendage in patients who are in the hospital with other problems,” says Dr. Deery, who is a hospital epidemiologist at Northern Michigan Hospital in Petoskey, Mich. “Physicians see an ulcer or a scab and they don’t delve into the extent of it to understand if there’s underlying osteomyelitis or not.”
What are some of the clinical signs that should make you suspect osteomyelitis? Dr. Deery says that if the ulcer has been present for more than six weeks and hasn’t improved despite appropriate wound care and off-loading, suspect osteomyelitis.
Other warning signs? Be wary of wounds that look chronic, necrotic and deep, even if you can’t feel bone. Toes that are swollen and sausage-like, Dr. Deery adds, are sometimes a very early warning of osteomyelitis.
2. Don’t be fooled by a negative X-ray. You probably know that if you can probe the bone in an infected foot ulcer, there is an 85 percent chance the patient has osteomyelitis. But what do you do when you suspect an infection, but you can’t probe the bone and the X-ray is equivocal?
Don’t assume that osteomyelitis isn’t present. It can take up to two weeks for signs of the condition to appear on an X-ray. That’s because significant bone destruction has to occur before plain X-rays can detect osteomyelitis. “Physicians don’t understand that this is the early phase of osteomyelitis and still needs to be treated with prolonged therapy,” explains Dr. Deery. “The horse is out of the barn long before you recognize anything is going on.”
That’s why following up with these patients in a few weeks is critical. If the ulcer doesn’t improve with good wound care, Dr. Deery says, order a new X-ray and compare it to the baseline film for more information.
3. Need more information? Think MRI, not nuclear imaging. If your first instinct is to order a nuclear imaging test when the X-ray isn’t clear, you need to rethink your approach. The IDSA guidelines—and everyone interviewed for this story—say that MRI is the preferred imaging modality to confirm osteomyelitis.
The problem with most nuclear imaging techniques, says Dr. Deery, is that they are sensitive but not specific. “They’ll light up because of any inflammatory changes in the small parts of the foot,” he explains.
Robert J. Snyder, DPM, a podiatrist and medical director of the wound healing centers at Northwest Medical Center in Margate, Fla., and University Hospital in Tamarac, Fla., says he sees many physicians take another equally inappropriate approach when the X-ray isn’t clear: They order a triple-phase bone scan.
He explains that the test is usually the wrong way to go because it depends on blood flow. As a result, it can lead to false positives—and unnecessary antibiotic therapy. “If you have a diabetic patient with peripheral vascular disease, you’re very often not going to get an accurate reading,” Dr. Snyder says. “It’s not a good test to hang your hat on, particularly in the diabetic population.”
And while MRI scans are expensive, Dr. Deery says the technology can provide a definitive diagnosis in difficult cases. And if you have a suspicious ulcer and can’t probe the bone and the MRI is negative, he says, the patient probably doesn’t have osteomyelitis.
Others, however, worry that physicians tend to overuse MRI in clear-cut cases of osteomyelitis. Elie F. Berbari, MD, a consultant in orthopedic infectious disease at Mayo Clinic in Rochester, Minn., says that when a patient with an infected ulcer is going to require surgical debridement, MRI technology will add little to the diagnosis.
“If an orthopedic surgeon is going to go in and debride the soft tissue and expose the bone and get biopsies of the bone,” he says, “why do you need an MRI? The orthopedic surgeons will go in there and expose the area and debride the infected bone to inspect it directly.”
4. Consider a bone biopsy. Most experts agree that when it comes to nailing down a diagnosis of osteomyelitis— and establishing a course of antimicrobial therapy— the gold standard is a bone biopsy.
“We’re taking care of patients who have been exposed to multiple antibiotics in the past and have had other infections,” says Dr. Halasyamani, who thinks that bone biopsies are underused by hospitalists. “These patients have been in the hospital many times and have been exposed to multiple courses of antibiotics for other reasons, so they’re at high risk for highly resistant organisms.”
And even if you’re sure the diagnosis is osteomyelitis, a bone biopsy will establish the bacteriology. It also gives the surgeon a chance to debride infected tissue and bone, which will help the wound heal.
Experts say it’s important, however, to get a culture that goes below the surface. Take a quick swab of the exterior part of the wound, for example, and you’re culturing what Dr. Snyder calls a “microbacterial soup.” Use that sample to determine the antimicrobial therapy, he says, and you’ll end up taking a broad-spectrum approach with just about every patient.
While a bone biopsy is the gold standard, there are alternatives in difficult cases. In some instances, for example, concerns about damaging the structure of an already compromised foot may make a strong case against the procedure.
In these cases, Dr. Deery says he asks his surgical consultants to perform a needle aspiration of the infected site, approaching the site from an area that is uninfected. This will provide not only a culture, but also histopathological information.
And while physicians often worry that a deep tissue culture may damage the foot, Dr. Deery says that both his personal experience and the literature say that there is little risk of damaging the foot with this procedure.
5. Tailor your antibiotic approach. While the literature suggests starting osteomyelitis patients on an empiric course of broad spectrum antibiotics, it’s important to tailor your approach once you get a culture.
“The worst situation you can find yourself in is that three or four weeks into a six-to-eight week program,” Dr. Deery says, “the patient develops an untoward reaction to the drug you selected empirically. Now you have no idea what to prescribe next because you don’t know what bug you’re treating.”
In Dr. Deery’s experience, more than half of the diabetic foot ulcers that are infected and have adequate blood supply to the foot contain gram positive organisms. “When you’re looking at cellulitis associated with a diabetic foot ulcer or infection,” he explains, “the appropriate antibiotic is usually an agent that covers Staphylococcus aureus or Streptococcus.”
If the patient presents with a gangrenous foot, on the other hand, you’re probably looking at a polymicrobial situation with gram negative organisms and anaerobes. Dr. Deery says that in these instances, you should probably lean toward broad coverage that will cover staff, strep, anaerobes and increasingly, MRSA.
Dr. Halasyamani says that when physicians think of treating osteomyelitis, they often think that a course of four to six weeks is necessary. But she and other experts agree that the time frame depends on how much infection is present in the patient.
“The duration of therapy for someone with osteomyelitis really depends on how much infected bone or soft tissue is left behind,” she says. “If someone has an amputation and all the infection is removed, that patient doesn’t need a lot of antibiotics. If you don’t do any surgery and residual infection remains, you need to prescribe three months of antibiotics.”
Dr. Berbari, who authored a section on osteomyelitis for PIER, the American College of Physicians’ Web-based decision-support tool, says that if a surgeon has removed the infected bone, perhaps in a partial amputation, antibiotic therapy must be adjusted accordingly.
“We have transformed the disease from a bone infection to a soft tissue infection. In this circumstance, I would give only two weeks of antibiotics. If the debridement is limited in trying to save as much limb as we can and osteomyelitic bone is left behind, then a four- to six week course is appropriate.”
6. Take a multidisciplinary approach. Experts worry that too many physicians think they can cure osteomyelitis with antibiotics alone, a notion that has received a growing amount of attention.
The IDSA guidelines note that some studies have presented evidence that in patients who could not undergo any form of surgery, between 65 percent and 80 percent beat osteomyelitis with up to six months of antibiotic therapy. Because there are questions about the methodology of those studies, however, most experts agree that osteomyelitis needs a multidisciplinary approach to be resolved.
“Treatment of osteomyelitis is really a combination of medical and surgical treatment whenever possible,” explains Dr. Snyder. “If a foot needs to be optimized from a vascular standpoint, there are methods to do that. If a patient has a deep space abscess, any infected tissue should be removed whenever feasible.”
He urges physicians to view both oral and intravenous antibiotics as suppressive, not curative, therapy in most cases. “Treating an osteomyelitis patient with only antibiotics is like treating a cancer patient with only chemotherapy,” Dr. Snyder explains. “It suppresses the problem and puts it into remission, but because of the immunopathy of these patients, the problem will recur.”
In some cases, he adds, doing nothing more than prescribing antibiotics can lead to a boomerang effect. While the wound gradually heals, Dr. Snyder says, it can create a fistula from the bone to the skin. “You wind up getting a track of puss that leads right back to the bone,” he explains.
Dr. Berbari says physicians have to realize the significance of diabetic foot infection and ulcers, which he describes as a marker of advanced diabetes. He notes that in one study, researchers found a 50 percent death rate one year after the diagnosis of an ulcer or osteomyelitis. That’s why he calls for a multidisciplinary approach to make sure nothing is missed.
“Osteomyelitis is telling us that this is diabetes that’s really advanced,” he adds. “There’s significant peripheral vascular disease that’s usually associated with heart disease and other complications of diabetes such as renal disease. By itself, it’s a bad prognostic marker of advanced problems.”