Background/Purpose:

Chronic non-bacterial osteomyelitis (CNO) is a rare condition characterized by inflammatory bone lesions with no detectable infectious agents. It may be unifocal (U-CNO) or multifocal (M-CNO) and have a monophasic or relapsing course. Various laboratory or imaging parameters have been proposed as possible outcome measures but none has been validated, yet.  

The present study was aimed to define the role of laboratory parameters and imaging tools (MRI and bone scinti-scan, BS) in detecting disease activity in patients with CNO.

Methods:

Patients with CNO, lasting longer than 6 months, were followed every 3-4 months. Laboratory inflammatory parameters (ESR, CRP, WBC, Hb, PLT, SAA), MRI and BS were performed at diagnosis, at the time of clinical relapse or at least yearly in all patients. Clinically, active disease was considered in presence of bone pain needing analgesics or second line therapy. Bone lesions were considered active on MRI in the presence of bone marrow edema (BME) associated to soft tissue inflammation (STI) including perilesional effusion and edema. As resulted in recent sport medicine studies (1), BME alone was not considered a parameter of activity (3). Disease activity at BS was defined by signal intensity, number and extension of hyperactive sites. A single radiologist and nuclear medicine practitioner, blinded on patients’ clinical status, reviewed all MRI and BS independently. Sensitivity, specificity and positive and negative predictive value (PPV, NPV) for disease activity detection of laboratory markers, MRI and BS were calculated by comparing data with clinical status of the patients at different time points.

Results:

16 CNO patients entered the study. 9 had UF-CNO, 7 had MF-CNO, mean age at disease onset  10,8 years (range 2.33-18.5), 54% were female. Disease duration at diagnosis was longer in patients with UF-CNO (14.2 vs 10.1 months). Localized bone pain was the leading symptom at onset in all patients; systemic symptoms, such as fever and fatigue, were more frequent in MF-CNO. At onset WBC was normal, CRP and ESR were elevated in 69.2%, especially in MF-CNO. After median 3 years follow up, 43.7% of patients had no symptoms and were off-therapy. At disease onset, all patients were evaluated by MRI and BS then, during the follow-up, 11 patients repeated BS once (T1), 13 patients repeated MRI once (T1) and 8 twice (T2). At disease onset, all 16 MRI showed BME with STI. Of the 21 follow up MRIs, 5 (23%) completely normalized, 7 (33%) showed only BME, 9 (42%) showed pathological changes. At disease onset all BS showed active lesions with mean 2.1 hyperactive sites (range 1-5). Of the 12 follow-up BS, 5 showed total remission, 3 partial remission and 4 persistent disease activity.

MRI sensitivity ranged between 0.83 and 1.00, specificity 1.00, PPV was 1.00, NPV ranged between 0.86 and 1.00. BS sensitivity was 0.83, specificity 0.74, PPV 0.76, NPV 0.80. Laboratory parameters correlated poorly with disease clinical status.

Conclusion:

MRI is a reliable tool for monitoring CNO in pediatric patients. BS overestimates disease activity, especially in UF-CNO. Laboratory inflammatory parameters are of limited utility. A validation study in a larger patients’ cohort is needed to confirm these preliminary findings.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/magnetic-resonance-imaging-is-a-reliable-tool-to-monitor-chronic-non-bacterial-osteomyelitis-in-children/