There's an old saying in medicine, "If you hear hoof beats, think horses not zebras." It means to look for the obvious not search for strange, unusual causes of symptoms. But in the case of hip pain in children, it may be a zebra like Lyme disease. Most of the time, joint pain caused by Lyme disease affects the knee. But in a small number of cases, Lyme arthritis presents only in the hip.
That's the conclusion of a group of pediatric orthopedic surgeons who studied their records of Lyme disease in children. Located in the northeastern region of the United States at the Children's Hospital, this hospital is in an area where Lyme disease is very high.
Yet out of all the children treated at the hospital, only 73 cases of Lyme disease were reported between 1995 and 2009. And only eight of those cases were hip pain caused by Lyme arthritis. The children in the study ranged in ages from three to 20 years old. The symptoms presented included hip pain (all eight children reported this), refusal to put weight on that leg (five children), and limp (three children).
Fever was not a key feature for most of the children. None of the families were aware of any tick bites or unusual skin rashes. But lab values were suspicious with elevated white blood cell count and sed rate (both indicators of infection and/or inflammation).
As a review of the records showed, special tests such as examining the joint (synovial) fluid gave a wide range of results even in known cases of Lyme disease. The test is still important to help rule out (or rule in) bacterial arthritis. All eight children also had a positive blood test for Lyme disease to help make the final diagnosis. In rare cases, a positive Lyme ELISA test can be a false positive.
Symptoms resolved in all eight children with treatment using antibiotics. The resolution of symptoms with antibiotics doesn't always confirm the diagnosis of Lyme disease. But given the symptoms and other clues (e.g., lab values), it is a telltale sign that Lyme disease was the cause of the hip pain.
The authors reviewed results from other studies and found that as many as 13 per cent of children with Lyme arthritis have hip pain. But in those other cases, the hip pain was part of several different joints that were affected at the same time. This type of Lyme arthritis is called polyarthritis. Hip pain as the only joint involved just isn't a typical early presentation of Lyme disease in children.
So when physicians are faced with hip pain, a limp, or refusal to put weight on the leg in children, it is better to look for horses (e.g., bacterial arthritis or synovitis) first before searching for zebras (Lyme disease). Either condition must be treated quickly and appropriately in order to get the best results. Whereas septic (bacterial) arthritis may need surgery quickly to save the joint, children with Lyme disease can be spared surgery and treated with antibiotics if and when properly (and quickly) diagnosed.
Reference: Michael P. Glotzbecker, MD, et al. Primary Lyme Arthritis of the Pediatric Hip. In Journal of Pediatric Orthopaedics. September/October 2011. Vol. 31. No. 7. Pp. 787-790.