Q: Your study looks at histology and culture analyses. What do these reveal?
A: A traditional culture helps you identify the bacteria, as well as guide your treatment when it’s tested against antibiotics.
A traditional histology allows the pathologist to look under a microscope for signs of osteomyelitis: Do they see the right inflammatory cells, white cells, lymphocytes, combinations of cells? Does this look like an acute or chronic osteomyelitis?
Q: Why might it be wise to combine culture and histology analyses?
A: If you have bacteria that’s difficult to culture via traditional methods, it may be a bacteria that doesn’t grow well or easily. If you combine culture with histology, pathologists can look and say, “Your culture was negative but we see these other signs, so we feel this is osteomyelitis.”
Q: Your study examined 35 consecutive patients aged at least 21 years who had moderate or severe infections bone infections in the foot linked with type 1 diabetes (n = 4) or type 2 diabetes (n = 31).
The samples were analyzed via culture, histology, and culture/histology examinations. You also performed genetic sequencing (quantitative polymerase chain reaction targeting 16S rRNA). How does this test fit in to bone biopsies in the clinic?
A: That’s a newer method and not a standard of care treatment for the diabetic foot. This analysis looks at DNA that’s present, bypassing the analysis of difficult-to-grow bacteria.
Q: What did you discover?
A: In this study, histology had the lowest incidence of positively detecting osteomyelitis. (45.7%). The level increases when a culture is taken (68.6% vs. histology; P = .02).
Then it goes up when DNA is used because it’s catching everything (82.9%, P = .001 vs. histology and P = .31 vs. culture).
[The study also found that adding histology to culture or to genetic sequencing did not change positive findings.]
Q: Does the study suggest one approach is better than the others?
A: This paper doesn’t provide enough evidence to use one method over another. The main purpose was to raise the concern that diagnosis can change dramatically depending on how the gold standard of bone biopsy is interpreted.
Q: What were the pros and cons of the genetic sequencing approach?
A: When we use this approach, our positive diagnostic rate significantly increases. But there are also downsides. We don’t know whether the bacteria we see is alive or dead. We just know it was there. So are the patients truly positive? That’s a question we can’t answer.
Genetic sequencing also doesn’t tell us about susceptibilities to antibiotics.
Q: What is the take-home message here for physicians who may order bone biopsies?
A: The thing to do is request both traditional culture and traditional histology.
As far as DNA sequencing, that not something I’d recommend as a standard of care.
Q: Can you comment on cost and insurance coverage for these approaches?
A: As far as I know, genetic sequencing is not covered as it is not standard of care in the diabetic foot and is used mainly for research at this time.