Intraop biopsy better for septic arthritis diagnosis

3 minute read

Relying on clinical features and lab tests leads to misdiagnosis or overtreatment, research suggests.

Tissue biopsy is a more accurate method of diagnosing septic arthritis and reduces the risk of overtreatment, according to an Australian study.

“The addition of culture from intra-operative synovial tissue biopsy increases the certainty of making the diagnosis of septic arthritis,” the Austin Health and University of Melbourne authors wrote in Rheumatology Advances in Practice.

“Diagnostic accuracy can be improved by taking a detailed history of relevant risk factors, collecting peripheral blood cultures, performing a timely joint aspiration before antibiotic exposure and having both an intra-operative synovial fluid and tissue biopsy collected.”

The Melbourne researchers said the accurate diagnosis of septic arthritis could be difficult and blood tests were often not reliable or specific for the disease.

Removing fluid from the joint to measure synovial white blood cell count and bacteria was also not a reliable diagnostic method, they said.

The study included 268 patients with suspected septic arthritis and the most commonly involved joint was the knee. They found that 85 had a confirmed diagnosis of true septic arthritis, and noted that few, if any, clinical factors at the time of presentation were useful in predicting this.

Laboratory investigations including median serum white cell count, CRP and ESR were higher among patients with true septic arthritis, but the results were broadly distributed and not statistically different between the groups, they said.

“There was also little difference in the pre-operative synovial fluid WCC, indicating its poor ability to discriminate septic arthritis from other pathology,” the researchers said.

Among 63 patients with negative synovial aspirate, biopsy specimens taken during surgery led to the diagnosis of six patients with true septic arthritis.

Positive synovial tissue biopsy was the only evidence of true septic arthritis in those patients, the researchers said.

“This would suggest that, for patients returning a negative pre-operative synovial aspirate, 10.5 patients would have to be sampled intra-operatively to diagnose one additional case of true septic arthritis.”

Of the 85 patients with true septic arthritis, 83 were given that diagnosis at discharge diagnosis and one was diagnosed with reactive arthritis.

However, of the 59 remaining patients, 27 patients were also discharged with a diagnosis of septic arthritis, and 26 were prescribed antibiotics “despite insufficient microbiological evidence,” the authors said.

The researchers said the study also confirmed previous studies that showed some risk factors might be helpful in increasing the pre-test probability of septic arthritis, including a history of IVDU, preceding trauma to the affected joint and positive blood cultures during admission.

Rheumatology Advances in Practice 2023, online 24 March

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