Metaphyseal changes on whole-body magnetic resonance imaging following bisphosphonate therapy in children with chronic nonbacterial osteomyelitis: distinguishing treatment effect from disease flare

Background Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory disease that often affects the metaphyses. Bisphosphonates, a second-line therapy, can cause bone marrow changes that may mimic active disease. Objective To characterize metaphyseal long-bone marrow changes on whole-body MRI (WB-MRI) following bisphosphonate therapy in children with CNO and evaluate if they can be distinguished from active disease. Materials and methods Retrospective study (2015–2025) included children with CNO treated with bisphosphonates and age- and sex-matched untreated controls. Two blinded pediatric radiologists independently evaluated long-bone metaphyses for CNO and bisphosphonate treatment effects classified as symmetric sclerotic bands, alternating high-signal and sclerotic bands, or predominantly high-signal bands. Associations with treatment, number of infusions, and intervals from the first to most recent infusions were evaluated, accounting for repeated examinations. Results Twenty-one treated children (median age 10.7 years, 12 females) underwent 30 pretreatment and 51 post-treatment WB-MRIs; 21 controls (median age 10.0 years, 12 female) underwent 48 examinations. Bisphosphonate-related changes occurred in 85.7% (18/21) treated children versus 14.3% (3/21) controls ( P <0.001). Sclerotic bands alone occurred in 23.8% versus 14.3%. Alternating high-signal-intensity and sclerotic bands (38.1%) and predominantly bright signal bands (23.8%) occurred exclusively after treatment. High signal was associated with more infusions ( P <0.001) from the most recent ( P <0.001) and first ( P =0.027) infusions and was most common around the knee and distal tibia. Conclusion Symmetric metaphyseal high-signal stripes are a dose- and time-related bisphosphonate treatment effect and should not be misinterpreted as active CNO. Sclerotic bands alone are not specific for treatment.