Issues And Answers In Diagnosing Diabetic Foot Osteomyelitis

Author(s): 
Kelly Pirozzi, DPM, and Andrew J. Meyr, DPM

Keys To The Microbiologic Analysis

Microbiologic bone culture for the diagnosis of diabetic foot osteomyelitis presents a unique set of challenges in terms of its reliability as a standard diagnostic procedure. The majority of diabetic foot wounds result from contiguous extension and therefore any sample runs the risk of contamination by contiguous soft tissues. Several studies have demonstrated that culture results from bone vary considerably from culture results of the tissue immediately surrounding bone.7-9 Additionally, culture results may misrepresent the number and type of infecting organisms within a sample. Whenever possible, one should utilize a transcutaneous biopsy through unaffected skin or only obtain specimens with a sterile instrument following complete debridement and irrigation.

   Another important consideration regarding the microbiologic analysis of a bone biopsy specimen is the variable time frames in which patients are off antibiotics prior to specimen collection. This could obviously have an effect on the culture and sensitivity analysis. There is no formal recommendation for how long a patient should be cleared from antibiotics for a valid sample and this is often unrealistic for a patient fighting acute diabetic foot disease.

What The Literature Reveals About Histopathologic Analysis

The histopathologic analysis also faces challenges with reliability and standardization. Our pathologist colleagues do not have a consistent classification for what they are looking at under that microscope. Through the limited clinical studies that have attempted to define bone samples affected by osteomyelitis, it is obvious that analysis is very subjective from a pathologist’s point of view.

   Highlighting this subjective component is a study from our hospital that attempted to quantify the reliability of the histopathologic analysis of bone with respect to the diagnosis of diabetic foot osteomyelitis.16 The study design consisted of four pathologists, blinded to previous reports, who attempted to place a bone specimen into one of three diagnostic categories: “no evidence of osteomyelitis;” “no definitive findings of osteomyelitis but cannot be ruled out;” or as “findings consistent with osteomyelitis.”

   Surprisingly, the results showed the pathologists to be in complete agreement with respect to the diagnosis in only 33 percent of the cases.16 Researchers also found that 41 percent of the time, one pathologist diagnosed a sample as no evidence of osteomyelitis while at least one other pathologist diagnosed that same sample as consistent with osteomyelitis. These results indicate that the use of histopathologic analysis for the diagnosis of diabetic foot osteomyelitis falls short of the “gold standard.”

   Further complicating matters is a 2011 study by Weiner and colleagues who examined cases in which clinicians attempted both histology and microbiology for diagnosis.17 They found that in 34 percent of cases, the microbiologic assessment was positive while the histopathologic assessment was negative or vice versa. In other words, the microbiologic and histopathologic analyses demonstrated much less than perfect agreement with each other.

A Closer Look At Consensus Findings For The Diagnosis Of Osteomyelitis

There is no doubt that the accurate diagnosis of osteomyelitis is necessary to ensure appropriate treatment and achieve successful patient outcomes. Recently, the International Working Group of the Diabetic Foot released a consensus statement and outlined a comprehensive diagnostic protocol for the diagnosis of osteomyelitis.2 In the creation of this protocol, the authors outlined different categories of confidence based on clinical, laboratory and imaging analyses.

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