Subclinical Enthesitis in Children with Chronic Nonbacterial Osteomyelitis

Objective: Enthesitis is rare in chronic nonbacterial osteomyelitis (CNO) compared to enthesi- tis-related arthritis. It may be asymptomatic in CNO patients. This study aimed to evaluate the presence of subclinical enthesitis in patients with CNO using ultrasonography (US). Materials and Methods: Patients with CNO were included in this study and evaluated with US by an expert pediatric radiologist. The entheses of 7 tendons were assessed bilaterally, includ- ing the common extensor and flexor tendons, the quadriceps tendon, the proximal and distal patellar tendons, the Achilles tendon, and the plantar fascia. Results: Fifty CNO patients were included. The median age of the patients was 12.4 years, and 58% were female. Subclinical enthesitis was identified in 3 patients (6%). These 3 patients were male, older than 6 years at diagnosis, had bilateral sacroiliitis, and were positive for human leukocyte antigen-B27. The enthesitis was located in the right quadriceps, right plantar fascia, and bilateral Achilles. One of these patients also had a clinical history of enthesitis at diagnosis. Treatment modification was not done when subclinical enthesitis was detected since they were in clinical remission and acute phase reactants were within normal limits. However, the patient with bilateral subclinical Achilles enthesitis had a disease flare afterward, and methotrexate was switched to etanercept. Conclusion: Subclinical enthesitis can be observed especially in CNO patients with overlappin- genthesitis-related arthritis features. The use of US may prove beneficial in detecting subclini- cal enthesitis and predicting disease flare.