The Classification Challenge of Pediatric Spondylarthritis

Given the efficacy of TNF-a inhibitors in adults with SpA, it is reasonable to predict that they will be beneficial in children. Indeed, small open-label studies of TNF-a inhibitors in pediatric patients with undifferentiated SpA have shown improvement in inflammation and the number of active joints and tender entheses.^30,31 However, concern over the risk of lymphoma and other malignancies means that every decision to use these agents must be an informed one. Assessing the actual risk of TNF-a blockade in patients with rheumatic and other inflammatory diseases has been confounded by the concomitant use of other medications and lack of uniform data collection. Additional data from postmarketing surveillance and registries will be important to determine long-term safety of these and other biologics. For now, the decision to use TNF-a inhibitors involves weighing risks with potential benefits in the treatment of what can otherwise be a very debilitating disease with potentially irreversible sequelae.

Separate classification criteria for pediatric SpA have been developed to recognize signs and symptoms of SpA that are more common in children and reduce reliance on clinical features reflecting axial disease that are frequently lacking. Although this is important to capture the broad spectrum of undifferentiated SpA, it has become increasingly important to identify children with undifferentiated SpA who also have axial involvement. The ASAS criteria for pre-radiographic axial SpA provide a tangible starting point, although it may be possible to relax the requirement for three months of back pain, because this symptom is unusual in children.

Prospects for Genetics

The discovery of several novel genetic polymorphisms that, together with HLA-B27, explain a large proportion of predisposition to AS, provide a unique opportunity to determine the value of these markers to predict outcomes and identify children who may benefit from early aggressive therapy.14 Until pediatric SpA classification is formally re-addressed, a reasonable interim approach might be hierarchical:

1. Identify children with juvenile AS (those under age 16 who meet the modified New York criteria);
2. Apply the ASAS criteria to identify axial SpA when possible; and
3. Use the ILAR system to identify undifferentiated SpA including both ERA and psoriatic arthritis.

Dr. Colbert is chief of the pediatric translational research branch at the National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health in Bethesda, Md.

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