Conference Coverage

Bone biopsy in suspected osteomyelitis: Culture and histology matter


 

EXPERT ANALYSIS FROM ADA 2018

Diabetic foot ulcers and infections can lead to osteomyelitis, a potentially devastating infection in the bone.

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How much of a difference can osteomyelitis make to a patient’s prognosis? A 2014 commentary by Benjamin A. Lipsky, MD, a prominent expert in problems associated with diabetic patients’ feet who’s with the University of Washington, Seattle, hints at the potential toll: “Overall, about 20% of patients with a diabetic foot infection (and over 60% of those with severe infections) have underlying osteomyelitis, which dramatically increases the risk of lower-extremity amputation” (Diabetes Care. 2014 Mar;37[3]:593-5).

Diagnosis of osteomyelitis, which relies on a bone biopsy, is clearly important. But there’s a big gap in diagnostic findings depending on whether doctors request culture or histology results, according to a new study released at the 2018 scientific meeting of the American Diabetes Association (Diabetes. 2018 Jul. doi: 10.2337/db18-110-OR).

Dr. Peter A. Crisologo, University of Texas Southwestern Medical Center

Dr. Peter A. Crisologo

In an interview, lead author and podiatrist Peter A. Crisologo, DPM, of University of Texas Southwestern Medical Center, Dallas, explained the study findings and offered guidance for requesting bone biopsies in possible cases of osteomyelitis.

Q: What makes diagnosis and treatment of osteomyelitis unique?

A: In the foot, there’s not a lot of soft tissue between the outside world and your bone. If the wounds on the feet go deep enough, they can spread a bacterial infection to the bone. This changes how foot infections are treated.

If you have a skin infection, it requires 11-12 days of antibiotics. Things start ramping up once you start getting into the bone. You’re talking potential surgery and 6 weeks of antibiotics through IV treatments. This is why it’s really important that you get your diagnosis right.

A lot of people say “I’m going to do the safe thing” and treat a bone infection with an extended course of antibiotics.

That’s not necessarily safe. If you’re overdiagnosing – for example, you identify bacteria that’s just a contaminant – you could put a patient through 6 weeks of IV treatment along with the risks of a PICC (peripherally inserted central catheter ) line infection, complications from IV placement, and complications from the antibiotic.

Also, acute kidney injury develops in at least a third of the patients who undergo 6 weeks of antibiotics. That’s not to mention the cost of the visits and the labs you have to draw. But we don’t want to underdiagnose either. If osteomyelitis is underdiagnosed and then not treated, the infection can smolder and continue to progress and worsen.

Q: Your study looks at the bone biopsy. How does it fit into care of osteomyelitis in the diabetic foot?

A: A bone biopsy is the standard for diagnosis under the guidelines of the Infectious Diseases Society of America/International Working Group on the Diabetic Foot (Clin Infect Dis. 2012;54[12]:e132-73 ).

But beyond that, nobody says anything. Everyone has an operational definition of how a bone biopsy is interpreted, and there’s a need for a consensus on how a bone biopsy can be used to diagnose osteomyelitis.

You’ll get different percentages of your patients diagnosed with osteomyelitis. For example, someone may say the biopsy is only positive if the histology is positive, while another says the histology doesn’t matter if the culture is positive.

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