- Volume 25 - Issue 11 - November 2012
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Likewise, for Khurram Khan, DPM, the accuracy of probe to bone depends on patient selection and "a little bit of common sense" as all the studies on probe to bone reveal a pattern. In studies performed on patients with infected wounds, he notes the positive predictive value of the probe to bone tests reaches the high 80s/low 90s percent range. In wounds that are uninfected the positive predictive value is approximately high 50s, but the negative predictive value was high 90s so in infected wounds, the test is highly sensitive and specific, notes Dr. Khan, an Associate Professor in the Division of Medical Sciences at the New York College of Podiatric Medicine.
In non-infected wounds, Dr. Khan notes if one cannot touch bone, then less likely the patient has osteomyelitis but if one can touch bone, he recommends following up with another study. The bottom line, he says, is one should utilize the probe to bone because it’s quick easy and does not cost anything. However, he cautions that the test is not the gold standard and one needs to add it to the rest of the history and physical to reach a diagnosis, possibly supplementing probe to bone with another exam to confirm diagnosis.
Under outpatient conditions, Dr. Wrobel says clinical prediction rules can help make up for clinicians’ inaccuracy. He notes magnetic resonance imaging “is still one of the best tests” for ruling out osteomyelitis while a bone culture is a good guide for medical management.
As for alternatives to probe to bone, long duration of the wound, wounds larger than 2x2 cm with significant depth and erythrocyte sedimentation rate of >65-70 can be a good predictor of osteomyelitis, notes Dr. Khan. He says diagnostic bone biopsy for both culture and histopathology is still the gold standard with MRI being the favored non-invasive exam. If MRI not available, he suggests a white blood cell labeled bone scan is the second best test based on 2012 Infectious Diseases Society of America (ISDA) guidelines.
"Understand that there is no single feature or physical exam finding or study which reliably excludes osteomyelitis. All of these are to be used together to help you reach a diagnosis," says Dr. Khan.
Dr. Wrobel also cites a study by Erdman and colleagues in Diabetes Care (http://tinyurl.com/c9tq5dn ) as “one of a few with a retrospective level of evidence for guiding medical management of deep infections.” In the that study, Wrobel notes that patients with intermediate composite severity index scores from 99mTc-WBC SPECT/CT hybrid imaging received six weeks of antibiotics and had a twofold better outcome than those not treated for this long regardless of bone involvement.
"Sometimes we focus so much on making the osteomyelitis diagnosis that we miss aggressively treating as deep infections," says Dr. Wrobel, which he says is supported by Lavery’s work validating the IDSA classification. He would like to see prospective studies from work using 99mTc-WBC SPECT/CT hybrid imaging.
The three Precision Intricast books on lower extremity biomechanics, authored by Kevin Kirby, DPM, are now available in Spanish. They are collections of Precision Intricast newsletters entitled Biomecánica del Pie y la Extremidad Inferior. For more information, visit http://www.dpmlab.com/html/bookreview.html .