by Scott Baltic

Last Updated: 2007-10-01 14:20:12 -0400 (Reuters Health)

NEW YORK (Reuters Health) – For the rare cases of prosthetic joint infection caused by rapidly growing mycobacteria (RGM), the preferred clinical approach is explantation of the prosthesis and prolonged antimicrobial therapy, according to a review by researchers at the Mayo Clinic.

In the September 15 issue of Clinical Infectious Diseases, the authors describe the cases of 8 patients who had developed 9 episodes of prosthetic joint infection between 1969 and 2006. The median age of the patients was 73 years.

Seven of the 9 episodes involved the knee, and one each involved the hip and elbow. Presentation was a median of 312 weeks (1-720 weeks) after prosthetic implantation, with symptoms of joint pain, joint swelling and fever. Diagnosis of RGM infection was made by culturing synovial fluid and periprosthetic tissue specimens.

All 8 patients underwent surgical debridement, and resection of the infected prosthesis was performed in 7 of the 9 joints. In addition, all patients received antibiotic therapy, for a median duration of 31 weeks.

After a median follow-up period of 33 weeks, no patients experienced clinical or microbiological relapse.

The two patients who retained their prostheses received multiple antimicrobial agents and were asymptomatic 24 and 189 weeks after debridement.

In a literature review, the researchers found 8 articles reporting 10 unique cases of prosthetic joint infection due to RGM. Seven patients underwent resection of the infected prostheses, 2 underwent debridement only and 1 had no surgical intervention.

Of all 18 patients, the report concludes, only those "who underwent removal of infected prosthesis were cured of infection and did not experience relapse after they completed antibiotic therapy. In contrast, patients with retained prosthetic components experienced relapse in the absence of effective antibiotic therapy."

Still, if resection is not feasible, the researchers note, RGM infections can be suppressed if the patient can be placed on a safe, effective and preferably oral regimen of antibiotics.

"Explantation of a prosthesis is not feasible in situations such as a severely ill patient who is not a good candidate for anesthesia and surgery," senior author Dr. Raymund Razonable told Reuters, "or a patient who has poor/weak bone reserve so that reimplantation of a functional prosthesis at a later time is not feasible."

Reimplantation should be the goal, the team advises, but in it was attempted in only 6 patients in this series and was successful in 2.

The authors conclude that prosthetic joint infection due to RGM is rare but should be suspected when routine cultures are negative. Key points of management include:

*Submitting multiple specimens for mycobacterial cultures.

*Choosing an antibiotic based on antimicrobial susceptibility testing.

*Delaying reimplantation till at least 6 months after resection.

Clin Infect Dis 2007;45:687-694.