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Board Review Diabetic Foot

Diabetic Foot Infections

Lee Rogers, DPM

Lee C Rogers, DPM reviews the 2012 Infectious Disease Society of America Clinical Practice Guideline for the Diagnosis and Treatment of Diabetic Foot Infections.

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Goals and Objectives
  1. Explain how to identify and properly diagnose a diabetic foot infection
  2. Explain how to obtain proper cultures from a diabetic foot wound
  3. Explain how to choose appropriate antibiotic therapy for diabetic foot wound
  4. Identify when surgical intervention is appropriate and necessary
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  • CPME (Credits: 0.75)

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    Release Date: 03/16/2018 Expiration Date: 12/31/2018

  • Author
  • Lee Rogers, DPM

    Medical Director
    Amputation Prevention Centers of America
    White Plains, NY

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  • Lecture Transcript
  • TAPE STARTS – [00:00]


    Lee Rogers: I’m Lee Rogers. I’m one of the co-chairs here. I’m also the executive medical director of our Amputation Prevention Center in Los Angeles, California and the medical director for the Amputation Prevention Centers of America which is a Restorixhealth company. I’m going to talk about diabetic foot infections and current treatments. The first and most important thing and I can just give you a review from what I’ve seen in the medicolegal arena. In the past five years, I’ve been an expert witness in about I think it was, last I checked, was 18 lawsuits. In those 18 suits, 13 of them dealt with infections and I only testify within my area of expertise, which is for limb salvage and 13 of them dealt with an infection in a diabetic foot. And every single time, this paper or depending on how old the alleged malpractice is, this paper or the previous version, which is published in 2004, if I’m on the defense side and we find that the doctor has really adhered to all the recommendations in this then we’re the one to bring it up. Sometimes it’s the plaintiff side that’s bringing it up saying that the doctor violated the standard of care because they weren’t adhering to this. And now these guidelines have been around in some sort or another from 2004 until now, this is the update in 2012, but this has really become the standard of care. And the standard of care is a legal definition that you’re held to that same standard in your community of what another reasonably qualified doctor of your specialty might do. And this is what we’re going to review in this talk is the 2012 IDSA Infectious Disease Society of America clinical practice guidelines for the treatment of diabetic foot infections. And we’re going to go through the most important parts of this. If you get this paper and if you don’t have it, my email address is at the end I think, email me and I will send you a PDF of this. But this paper is about 60 pages long, but the first eight pages are the executive summary. And it summarizes everything you need to know about how many pages there are and they’ve reviewed over 400 references to come up with this. So we’re going to look at the executive summary in detail and I’m going to basically tell you what this says about the diagnosis and treatment of diabetic foot infections. The way that they did their executive summary was a series of questions and these are the commonly asked questions by people who want to know what’s the best thing to do for diabetic foot infection. So in which diabetic patients with a wound should I suspect an infection and how should I classify it? The major points here is that evidence of infection generally includes classic signs of inflammation, so redness, warmth, swelling, tenderness or pain or purulent secretions, but may include some secondary signs and symptoms. And factors that increase the risk for diabetic foot infection, our probe-to-bone test if it’s positive, an ulcer that’s present for more than 30 days, history of recurrent foot ulcers, traumatic foot wound, presence of PAD in the affected limb, and the previous history of an LEA, lower extremity amputation. So how should I assess a diabetic patient presenting with a foot infection? So we need to diagnose the infection based on the presence of at least two classic symptoms or signs of inflammation so these were stated before erythema, warmth, tenderness, pain or induration or purulent drainage. And it’s also important to note that infection is entirely a clinical diagnosis in the diabetic foot. There’s not a single test you can do that can diagnose an infection. Tests are helpful, but they will not be the diagnostic that you’re looking for. White blood cell count, for example, is only elevated in 56% of those with diabetes that have moderate or severe infections. And if this is something that is used as an admission criteria from the emergency department, for example, then you’re going to not be admitting a lot of infections that require admission. So you can look at the white blood cell count, but you have to realize that because of the immunopathy and diabetes, it’s not elevated in about half of patients.

    [05:03]

    And likewise a culture is not a test that you used to diagnose an infection and I’ve dealt with, in some cases, wound care centers where they have standard protocols. Any new patient that comes in, they get a culture regardless of whether or not it’s infected and that’s wrong and it actually hurts you in a liability sense because you know it’s not infected. You’re going to take this culture. You can culture your earlobe or your elbow and it’s going to grow something because there’s bacteria everywhere. And so if you swab a wound, you’ll get a positive culture. And then when you get that result you’re faced with the choice, what do I do about this? Do I either put them on an antibiotic that they don’t need or not. And it’s most appropriate to not, but if you do that, you need to document it because you don’t know what’ll happen in six months from then, maybe the patient gets an osteomyelitis and has their limb amputated and they didn’t like your staff because they were rude and they want to sue now. And so now some lawyer who is looking through the records and finds a culture on the chart. This has happened to me numerous times. They find a culture on the chart from six months earlier that really has nothing to do with the osteomyelitis or the amputation, but they try to make a case to a jury that you failed to treat an infection and that seeded in osteomyelitis. So it’s really important to only culture infected wounds and not use it as a diagnostic test for infection. Instead if it’s infected and you make that diagnosis, use the culture as the test to determine whether or not you put them on the right antibiotic. Then you need to document and classify the severity of the infection. The most widely known and probably the easiest to use and one that also has the most amount of evidence is the IDSA zone classification for diabetic foot infections and that’s highlighted there in red. It’s broken up into four classes, uninfected, mild, moderate, and severe. An infected wound is obviously no sign or symptom of infection, mild infected wound is only local manifestations of infection less than two centimeters of surrounding cellulitis or erythema, no deep spread, moderate infection is greater than two centimeters of surrounding erythema, could be deep spread such as down to bone or tendon even an osteomyelitis, but there’s no systemic response from that. So you’re not looking at a fever, chills or elevated white blood cell count or any of the other systemic responses you might see. And then a severe infection is the same as a moderate infection except there is SIRS, stomach inflammatory response syndrome or sepsis and you can see by either a temperature greater than 38 or less than 36, heart rate greater than 90, respiratory rate greater than 20. In those cases either an elevated or decreased white blood cell count or more than 10% bands. They recommend that assessing the affected limb and foot for arterial ischemia such as Dr. Freiburg just spoke about. But looking at this classification, the IDSA classification, this was validated by Lavery and Armstrong. The classification is on the bottom, no infection mild, moderate, and severe. And then you see the rate of hospitalization and amputation in yellow and in red. There’s something that happens between a mild and a moderate infection that drastically increases the risk of hospitalization and amputation. So if you can keep your patients either uninfected or only mildly infected according to this classification, then you can keep them out of the hospital and hopefully avoid an amputation. But this validated that this classification is a useful classification to not only something to memorize, but it also predicts the outcome and it also helps you to choose your therapy. So in which patients’ with a diabetic foot infection should I hospitalize and what criteria do I need to meet before I discharge them? The panel recommended that all patients with severe infection and a moderate infection with complicating factors are hospitalized. When should I obtain a specimen for culture from a patient with a diabetic foot wound?

    [09:58]

    For clinically unaffected wounds, the recommendation is, do not culture. If it’s not infected or didn’t meet those criteria, didn’t have two or more of those signs that we mentioned earlier, redness, swelling, pus, then no culture. For infected wounds, clinicians need to take an appropriate specimen and this is not just a, what we call swabbing the wound toilet, where you take a swab and you run it around the wound and you send that off for culture. You want to debride the wound, take some of the tissue at the base of the wound and send it because that’s the real pathogen that’s causing the infection, so whether that may be with a curette where you’re curetting the base of the wound and then you have some material that’s inside of the curette scoop and you take the cotton swab and swab it out to put it in the culture tube, that’s fine or you take a little biopsy or you use a scalpel and remove some tissue. But whatever it is, you need to actually remove deep tissue and not just swab the superficial skin. Here is the table with recommendations for cultures and this is really important. I use this in almost all of my lectures. The focus is on infection, in general, but this is important because again like I said from a medical legal standpoint, this can save you a lot of headaches. This got the do’s and don’ts. So do obtain an appropriate specimen for culture from almost all infected wounds, do clean and debride the wound before obtaining your specimen for culture. Do obtain a specimen by either scraping, using something sterile to scrape the base of the wound. You could also aspirate purulent secretions and you could send that if you wanted to. But do not culture clinically uninfected wounds, do not obtain a specimen without first cleaning or debriding the wound, and then do not obtain a specimen by just swabbing the wound or the wound drainage. So when should you consider imaging studies to evaluate for a diabetic foot infection and then which type of study should you use? So the panel recommends that all patients who present with a new diabetic foot infection have at least plain radiographs of the affected foot which might look for subcutaneous emphysema or signs of osteomyelitis. They also recommended that the MRI is really the study of choice for patients when you need something more sensitive or more specific, specifically looking for osteomyelitis or for abscess. How do you initially select and when should you modify an antibiotic regimen for a diabetic foot infection? The clinically uninfected wounds should not be treated with an antibiotic and that sounds like common sense and it’s just unfortunate that common sense is not so common. People should not use antibiotics on uninfected wounds. That includes topical antibiotics and that leads to resistance and can cause a lot of complications. Selected empiric antibiotic regimen based on the severity of the infection and I have a table on how to do this. But your first choice of an antibiotic is going to be empiric. You do not know what the bacteria is that is causing this infection. You sent a culture for specimen, but that’s going to give you a result in three days, but you have to guess on what the bacteria is causing the infection. Now there are things that will clue you into which bacteria it is and we’ll talk about those, but you’re still guessing. So here’s their general recommendations without providing specific antibiotic names. For mild and moderate infections in patients who have not recently received antibiotic treatment, they suggest that the therapy target just aerobic gram positive cocci. So that’s really in most cases just staph aureus and streptococcus for these patients with a mild or moderate infection. For most severe infections, the panel recommends starting broad-spectrum empiric antibiotic therapy pending the culture results and the susceptibility data. And then also there’s a lot of confusion of when to use an antibiotic for pseudomonas, but the panel recommends that empiric therapy directed at pseudomonas is usually unnecessary except for patients with risk factors for true infection with the organism.

    [14:55]

    And then regarding MRSA, consider providing empiric therapy directed at MRSA in a patient with a prior history of MRSA or when the local prevalence of MRSA colonization or infection is high or the infection is clinically severe. And the way you can find out what your local prevalence of infection is, if you’re in a hospital, you’ve admitted somebody, you can ask the hospital, the microbiology department, you can ask them for your antibiogram and it’s like a telegram except it’s got your bacteria on it, but you’re asking for your antibiogram and they give you for the past six months, they’re all acquired to keep this. So they give you the past six months of all the bacteria that were grown out in culture and they will tell you what percent of your staph aureus isolates were MRSA and if you have a greater than 50%, which we do in a lot of hospitals and including ours. If you have a greater than 50% MRSA ratio for your staph aureus isolates, then you should be using empiric antibiotics geared towards MRSA from the beginning because it’s more likely MRSA than not, but you can find that out with your antibiogram. Definitive therapy should be based on the results of an appropriately obtained culture and sensitivity and this is difficult if you didn’t obtain the culture and sensitivity yourself, it was down in the emergency department and maybe one of these swab cultures that’s not really reliable. You’re going to have to take that into account when you’re choosing your definitive therapy. They recommend parenteral therapy for all severe and some moderate diabetic foot infections at least initially and then switch to oral agents when the patient is systemically well. And for how long patient should need antibiotic treatment? The initial course of antibiotics for soft tissue infection of about one to two weeks for mild infections and two to three weeks for moderate or severe infections. Here’s the basic diabetic foot infection pathway. You have mild on one side, you have moderate and severe on the other side, on your right side. Let’s follow the pathway down on the mild. So on mild infections, just require a gram-positive coverage. You send a CNS at that point. With gram-positives, again like we said, just because it’s a mild infection, it doesn’t mean it’s not MRSA, so you need to ask about risk factors for MRSA and those include recent multiple antibiotic use, history of MRSA probably the highest risk factor, MRSA in the family or if you look at your antibiogram and you see that there’s a high prevalence of MRSA in your community. Then those patient if they have risk factors can be treated with any one of these drugs, Bactrim, Levoquin, in some cases Zyvox (linezolid), but they should use clindamycin, and I’ll show you why in a second. If there aren’t risk factors for MRSA, then you can do a penicillin derivative cephalosporins or clindamycin. Let’s follow the moderate or severe pathway for a second. These are polymicrobial infections. You send your CNS, you need MRSA de-escalation and that’s where you start out with a broad-spectrum anti-MRSA medication and then you narrow it down after your culture and sensitivity comes back. This is like linezolid which is Zyvox plus a gram-negative, Vancomycin plus double covering for methicillin-sensitive staph aureus and adding a gram-negative agent or Tygacil. This is not an exhaustive list. This is what we’re using in our hospital, and you can do the same thing. You place them into these categories based on whether they’re broad-spectrum anti MRSA or not. But the reason why we don’t use the clindamycin in cases of suspected MRSA is that there’s a one step resistance for MRSA to become resistant to the macrolide even if you’re looking at your culture and sensitivity. It shows that it’s sensitive for clindamycin. That’s called the D-test. You may see that being reported. The reason why they call it a D-test, if the D-test is positive that means it’s going to be a clindamycin resistance. They call it a D-test because when it plates out, it looks like a capital D on the plate. How should I diagnose and treat osteomyelitis in the foot in a patient with diabetes? So you need to consider osteomyelitis as a potential complication of any infected deep or large foot ulcers. Doing a positive probe-to-bone test is also suggestive of osteomyelitis. When diagnosing, using a diagnostic imaging for diabetic foot osteomyelitis, recommend the MRI. In that case, you have to be careful in patients with Charcot foot or if you’re trying to differentiate between Charcot and osteomyelitis, that’s very difficult to do for a radiologist who doesn’t have a clinical background on what’s going on with the patient. And in fact, you have to look at secondary signs and symptoms of the clinical aspect to help guide you on whether or not there is osteomyelitis or Charcot foot present.

    [20:04]

    And they also suggest the most definitive way to diagnose diabetic foot osteomyelitis is by the combined findings on bone culture and histology. That doesn’t mean we always do it, but that is the most definitive diagnosis. You need to consider primary surgical or primary medical strategies for the treatment of diabetic foot osteomyelitis in properly selected patients and after a radical resection leaves no remaining infected tissue. So you have a TMA. You do TMA for osteomyelitis of the forefoot. Forefoot is gone, there’s no infected tissue left over. Some people erroneously will place the patient since they had osteomyelitis on four to six weeks on a PICC line with an I.V. And really what you need is just soft tissue coverage for a short duration. You can see even just two to five days for those patients because you’ve removed the infection. In which patients with a diabetic foot infection should I consider surgical intervention and what type of procedure is appropriate? Urgent surgical intervention is required for diabetic foot infections accompanied by gas in the deeper tissue, abscess or necrotizing fasciitis and then less urgent surgery for wounds with substantial non-viable tissue or even bone or joint involvement. Recommend involving a vascular surgeon early on whenever ischemia complicates diabetic foot infection, however, note that infection always trumps vascular in the diabetic foot if you have an infected dysvascular foot. It is most important to take care of the infection first and that means if you’re taking them to the operating room before they get “vascular clearance” that’s fine, that’s appropriate, that’s what you’re supposed to be doing. Operating room, remove the infected tissue, vascular surgeon can see them the next day, and that’s most appropriate because the infection is the emergency and the vascular can wait the one day. Why that my residency director used to always teach us this? What’s the one antibiotic with no resistance? This comes from Mike Delacourt [Phonetic] and you’ll know it when you see it, the surgical scalpel. That’s true. Infections are treated surgically and in some cases even MRSA abscesses, small abscesses for young people who are athletes have been treated solely with an I&D and found a resolve just with the I&D alone. This is really important. What types of wound care technologies or techniques and dressings are appropriate for the diabetic foot wound? So it’s not only about the infection. And just a few about 30 minutes ago, Bob was saying it’s not only about vascular disease, in fact that we have all these things that come in together that need to be taken into consideration. But in addition to managing the infection, we have to make sure that we’re doing regular periodic debridement. You have to do offloading. You have to select a dressing that allows for a moist wound healing environment, but controls the excess exudate and then no topical antimicrobials for clinically uninfected wounds. There are some adjunctive therapies that could be used in select diabetic foot wounds; bioengineered skin equivalents, growth factors, G-CSF, hyperbaric oxygen, and negative pressure wound therapy are all adjunctive therapies that are used after the diabetic foot infection in order to heal the wound. In the few remaining minutes, we’ll go over a couple of cases and show how you can use the algorithm to make your decisions. So this lady comes in with a severe diabetic foot infection, she has fever, chills, malaise, she does have an elevated white blood cell count slightly. This is classified as IDSA severe and it’s limb threatening, so this is an emergency. How are we going to start out with her as we follow the severe pathway? We do polymicrobial coverage, MRSA de-escalation, and in her case, we’re using Tygacil (Tigecycline). We start with 100 milligrams I.V. time 1 then 50 milligrams I.V. every 12 hours. These are the same precautions as tetracycline. They have the same precautions as other tetracyclines. They cause a lot of nausea and vomiting.

    [25:01]

    In one study, 18% nausea and vomiting, not only nausea, but actual vomiting. In some of our patients with this, we’ll pre-treat with Zofran. There’s no oral equivalent to this directly and this has a black box warning now for an increase in the mortality rate in patients with severe infections. So you have to be aware of that. We have this lady, we use our one antibiotic that has no resistance and remove everything that’s infected to begin with. She’s placed on her broad-spectrum therapy, get her culture back. Three days later, you can see here, she’s got negative blood cultures. There’s the Penicillin line and you can see it’s sensitive, so she has a methicillin-sensitive staph aureus that’s causing this infection. We have her on Tygacil at the moment. As long as she’s in the hospital, we’ll change to Unasyn and then when she’s discharged, she’ll go on to an oral Augmentin. Another case, a 45-year-old male with type 2 diabetes, infected hallux ulcer, no systemic signs, but has risk factors for MRSA and white blood cell count that is bordering normal. I think ours was 10.8 or so was our upper limit of normal. This extends more than 2 centimeters from the surrounding wound. So this is an IDSA moderate infection. We start out again on the moderate severe pathway. He was started on Vancomycin. Culture comes back three days later and you can see here that it is MRSA and it’s sensitive to linezolid, which is Zyvox. But here’s the thing I was talking about before, you can see here how it says resistant, look below that dotted line, it says resistant to erythromycin, but sensitive to clindamycin and people sometimes misinterpret this. This is one of those cases where you’ll get resistant to clindamycin then within 24 hours. It’s inducible resistance for clindamycin. If you just looked at this and said, “Oh, great, clindamycin great choice,” safe drug, put him on clinda, but it’s not going to work and in fact be even worse for them. So linezolid Zyvox send them home. Here’s the D-test. So they came up on the wrong slide. This is the right slide, sorry. The negative D-test, I can’t use the pointer, but on the left hand side you have clindamycin and erythromycin disks and this is the bacteria that’s plated out, in this case it’s MRSA. And then on the right-hand side, you have the erythromycin disk, which is completely covered with bacteria. So it’s resistant to the erythromycin. But the bacteria instead of being a nice circle all the way around, the clindamycin disk the bacteria once it’s exposed to a macrolide, it can become resistant and it encroaches upon the clindamycin disk and it looks like a capital D. So it’s called the positive D-test. And then here we are, resolution of infection. He was on vancomycin, go home now on Zyvox. And in these cases, you know, moderate or severe infections two to three weeks of antibiotic therapy. Here’s my email address, if you want a copy of this paper, which really goes into a lot more detail than this, but the executive summary like I said is the first eight pages, a very thorough review of what you need to do to treat a diabetic foot infection. So thank you very much.

    [Applause]


    TAPE ENDS - [29:21]