Pediatric Lyme Arthritis Twice as Common as Septic Arthritis in Endemic Areas of Lyme Disease

Fran Lowry

March 15, 2010

March 15, 2010 (New Orleans, Louisiana) — Almost half of children with fluid in the knee in the Northeastern United States are likely to have Lyme arthritis, according to a new study presented here at the American Association of Orthopaedic Surgeons 2010 Annual Meeting.

"In a pediatric population, Lyme arthritis is probably the first diagnosis to consider if you are in an endemic area," Matthew D. Milewski, MD, from Yale–New Haven Children's Hospital in Connecticut, told meeting attendees.

Connecticut has the highest rate of Lyme disease, but other areas of the United States are considered endemic, including the northeast from Maine to the mid-Atlantic states, Minnesota, Wisconsin and other Midwestern states, and Northern California.

Lyme arthritis is on the rise, increasing almost 100% in the past 15 years, according to data from the Centers of Disease Control and Prevention.

Children are nearly twice as likely to develop arthritis with Lyme disease than adults, and also to have it as the initial manifestation. Distinguishing children who have Lyme arthritis from those who have septic arthritis can be a challenge in the emergency department (ED), but doing so is essential because their treatment is so different, Dr. Milewski said.

"In Connecticut, where Lyme disease is endemic, a lot of kids would come into our [ED] with a swollen joint, and we would be forced to try to decide whether this person had septic arthritis or Lyme arthritis," Dr. Milewski told Medscape Orthopaedics. "Septic arthritis is traditionally considered a surgical indication in most cases, and Lyme arthritis is considered something that can be treated with antibiotics. This is a big difference in treatment options and we wanted to help the providers in the [ED] try to decide between these 2 courses of treatment."

In their study, Dr. Milewski and colleagues sought to determine how often children presented with Lyme arthritis at their center, and how they differed from children with septic arthritis.

They undertook a retrospective review of all joint aspirations done from January 1992 to April 2009 in children younger than 18 years. They collected data on cell count, fluid differential, culture, hematologic inflammatory markers (including peripheral white blood cell count, peripheral blood differential, erythrocyte sedimentation rate, and C-reactive protein), and Lyme disease serological testing.

They also reviewed charts for the presence of fever and weight-bearing status at the time the children presented, and for radiographic or ultrasound evidence of effusion.

Of the 391 patients who were analyzed, 123 (31%) tested positive for Lyme disease and 51 (13%) had septic arthritis.

They also found that children with septic arthritis had a higher nucleated cell count than those with Lyme arthritis (123,000 vs 60,200 cells/mm; P = .007).

They were also more likely to have fever. Twenty-seven of 49 septic arthritis patients (55%) had temperatures of at least 101.5 °F, as did 26 of 120 Lyme patients (22%); 33 of 49 septic arthritis patients (67%) had a low-grade fever, defined as a temperature of at least 100.4 °F, as did 46 of 120 Lyme patients (38%).

Both of these temperature cut-offs were found to be significantly different between the 2 cohorts (P < .001 and 0.001, respectively).

In addition, virtually all of the children with septic arthritis refused to bear weight, compared with only 39% of the children with Lyme arthritis (< .001).

Erythrocyte sedimentation rate and C-reactive protein values were similar in the 2 groups and did not help to distinguish between them, Dr. Milewski noted.

This study gives providers more tools to help determine their course of treatment, Dr. Milewski told Medscape Orthopaedics.

"We don't have a rapid Lyme test that helps the care provider at the point of initial presentation to decide if this is Lyme or not, but this information gives us a way to start to lean a practitioner one way or the other if they are on the fence. It speaks to the fact that Lyme disease is so common that it really needs to be considered every time you evaluate a kid for septic arthritis."

Commenting on this study for Medscape Orthopaedics, Theodore J. Ganley, MD, director of sports medicine at the Children's Hospital of Philadelphia and associate professor at the University of Pennsylvania School of Medicine in Philadelphia, agreed. "The emphasis from this study is that if you have a child with a mild injury and you have a significant knee effusion that is atraumatic or with minimal trauma, for these kids you really need to consider Lyme and test for Lyme."

He called the study helpful to clinicians because it raises awareness about the "fairly high" incidence of Lyme arthritis. "This is not a rare, reportable case. The incidence is very real."

Dr. Milewski and Dr. Ganley have reported no relevant financial relationships.

American Association of Orthopaedic Surgeons (AAOS) 2010 Annual Meeting: Abstract 141. Presented March 10, 2010.


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