Very few children with the main complaint of knee pain referred to pediatric rheumatologist are likely to be diagnosed as juvenile idiopathic arthritis (JIA), according to a study published in the March 2023 issue of The Journal of Paediatrics and Child Health.¹ The presence of limping and elevated laboratory markers of acute inflammation such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were strongly associated with the diagnosis of JIA.

In this single-center study, researchers retrospectively analysed medical records of 262 children with a complaint of knee pain. These children had been referred for paediatric rheumatological evaluation between October 2012 and June 2019. They were categorized into four groups: 32 children (12.2%) had confirmed JIA, 46 (17.6%) had inflammatory knee pain other than JIA, 57 (21.7%) had non-inflammatory knee pain, while in 127 children (48.5%), no musculoskeletal disorders were diagnosed. Infection-related arthritis and Lyme arthritis were the most frequent types of arthritis in children with inflammatory pain.

Compared to the other three groups, limping was more common in children who were diagnosed with JIA (84.4%); they were also found more often to have joint swelling (65.6%), decreased range of motion of the knee joint, both passive (71.0%) and active (77.4%). More than half (54.4%) of patients with non-inflammatory pain had significantly increased pain after physical activity vs the JIA and no disorders diagnosed groups. Patients with inflammatory knee pain had significantly less difficulty in climbing stairs than those with JIA or non-inflammatory pain.

On multivariate analysis, patients with inflammatory pain had pain in multiple joints and a positive family history of autoimmune diseases (39.1% vs ~22% in JIA vs 14% in non-inflammatory pain). Limping was absent in patients with non-inflammatory pain; pain in joints was limited to the knee and pain increased in intensity after physical activity in this group. Limping and ESR ≥10 were the risk factors in the JIA group.

Among children in the no disorders diagnosed group, the indicators were CRP < 5 mg/L, no increase in pain after physical activity and ultrasound showed no musculoskeletal abnormalities.

Children with JIA were significantly younger than those in other groups with a mean age of 5.1 years vs 13.7 in inflammatory pain, 14.4 in non-inflammatory pain and 11.8 years in children with no disorders diagnosed. The JIA group also had leukocytosis, thrombocytosis, decreased hemoglobin and hematocrit levels and increased ESR and CRP levels.

“There is a need to identify specific factors that may indicate JIA as opposed to other causes of knee pain”, note the authors. This study has attempted to characterize knee pain in children and provides “clinical clues”, which can help the primary care physician to decide if these children need a rheumatological consultation. Seventy percent of children with knee pain, in this study, either had non-inflammatory pain suggestive of a mechanical pathology or had an indeterminate etiology. Only a little more than 10% children, who were among the youngest, had a confirmed diagnosis of JIA in this study indicating that “knee pain alone, as a chief complaint, rarely leads to a final JIA diagnosis”. It highlights the significance of a “well-documented medical history and detailed clinical examination” when examining a patient with knee pain.

Reference

1. Daiva Gorczyca, et al. Knee pain as a reason for referral to a paediatric rheumatologist: A retrospective study. J Paediatr Child Health. 2023 Mar;59(3):439-444. doi: 10.1111/jpc.16309.