Ustekinumab as a novel treatment of chronic nonbacterial osteomyelitis: a case report.

Background: Chronic nonbacterial osteomyelitis (CNO) is a rare inflammatory disorder that commonly causes bone destruction in the metaphysis of long bones, pelvic and vertebral bones, the clavicle, and the mandible. CNO is often misdiagnosed and underreported. This presentation of debilitating back pain caused by CNO showcases diagnostic challenges and potential for novel therapeutic treatment. Case Description: A 14-year-old male with Crohn's disease presented with acute, worsening lower back pain and two months of hematochezia after recently stopping infliximab. Physical examination showed sacral tenderness, diffuse erythematous lesions, normal strength and no focal neurological deficits. A T2 hyperintense mass at S4 on magnetic resonance imaging (MRI) was identified. Skeletal survey was negative; however, repeat MRI indicated phlegmon and epidural abscesses suggestive of osteomyelitis. Initial treatments with intravenous cefazolin and oral minocycline were ineffective, leading to interventional radiology (IR) guided S1 biopsy that revealed fibrous tissue without signs of infection. A left L5-S1 laminotomy and microdiscectomy were performed with surgical pathology of the L5-S1 disc showing focal acute inflammation with no evidence of microorganisms, leading to a diagnosis of CNO. Despite surgery, he experienced worsening pain and gait difficulties. After starting Ustekinumab for Crohn's disease, his back pain and mobility significantly improved, and he returned to school. Follow-up MRI showed improvement in the epidural swelling, decreased enhancement of the lumbar and sacral canal extending from L4-S3, and significantly decreased osseous enhancement at S1. Conclusions: This case illustrates an unusual manifestation of CNO with an S1 vertebral lesion. The initial MRI findings and failed treatment with antibiotics resulted in a diagnostic challenge leading to an invasive workup involving multiple biopsies to rule out infection and malignancy and a subsequent L5 laminotomy and microdiscectomy. The timing of symptom onset following cessation of infliximab suggests a Crohn's flare likely triggered CNO. The soft tissue abnormalities noted on imaging were likely secondary inflammatory changes associated with the vertebral lesion. The resolution of back pain with ustekinumab is in line with other cases of successful resolution of CNO with biologic agents and supports the theory of shared pathophysiology in CNO and inflammatory bowel disease (IBD).