The objective of the study is to establish a prospective disease registry for chronic recurrent multifocal osteomyelitis (CRMO)/chronic nonbacterial osteomyelitis (CNO) in order to investigate the natural history of the disease and the responses of patients to different clinical managements over 10 years.

Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disease that mainly affects children and adolescents. Clinical presentations range from mild and sometimes limited unifocal disease to severe, chronically active or recurrent inflammation of multiple bones. The latter is referred to as chronic recurrent multifocal osteomyelitis (CRMO). Here we will use the term "CNO" to refer to the entire spectrum of this disease. CNO can be complicated by vertebral compression fractures, kyphosis, and leg length discrepancy when it is not recognized early or treated adequately. The diagnosis of CNO is made by excluding alternatives in the differential diagnosis including malignancy (leukemia, lymphoma, and primary or metastatic bone tumors), Langerhans cell histiocytosis, and infection. Clinical assessment in conjunction with serum inflammatory parameters and imaging studies, particularly magnetic resonance imaging (MRI), are crucial for the diagnosis and monitoring of disease activity of CNO1.

Because of significant variation in clinical treatment practices among pediatric rheumatologists, standardized treatment regimens (consensus treatment plans, CTPs) have been developed within the Childhood Arthritis and Rheumatology Research Alliance (CARRA), a North American organization comprised of pediatric rheumatologists and researchers, for CNO patients with an NSAID-refractory course and/or with active spinal lesions2. These CTPs provide an opportunity for pediatric rheumatologists to conduct comparative effectiveness research on CNO through prospective data collection. CRMO/CNO workgroup is comprised of pediatric rheumatologists from North America as well as international colleagues who are interested in collaborating in CNO research. Furthermore, risk factors of severe disease have been described by Wipff et al. based on a large retrospective cohort study3. Their results may be validated by an independent prospective cohort study. To date, there has been only one prospective study on CNO since its first description in 19724. Therefore, we propose to establish this international registry of patients with CNO to accomplish above goals. Long-term outcomes of CNO remains unknown due to the lack of prospective study. It has been estimated that at least 50% of CNO patients continue to need medications for CNO during adulthood. Our study will collect the clinical data and provide valuable data to characterize the long-term outcomes.

Inclusion Criteria:

• - Age at enrollment is equal to or younger than 21 years of age
• Presence of bone edema on STIR or T2 fat saturation sequence on MRI within 12 weeks of enrollment
• Whole body imaging evaluation (either WB MRI or bone scintigraphy)
• Bone biopsy to exclude infection or malignancy unless bone lesions follow typical distribution or there is IBD, psoriasis, or palmar plantar pustulosis

Exclusion Criteria:

• - History of or current malignancy
• Current infectious osteomyelitis
• Contraindication to the selected treatment agent

Children with a diagnosis of CNO/CRMO who have failed NSAIDs and/or with active spinal lesion