Chronic Non-Infectious Osteomyelitis of the Petrous Bone: A Case Series

Objectives Chronic Nonbacterial Osteomyelitis (CNO) is an autoinflammatory disorder of bone typically beginning children between the ages of 7-12. Any bone can be affected, involvement of the skull is unusual and petrous bone involvement has not been reported. The objective of our study is to illustrate presenting features associated with CNO of the petrous temporal bone, its treatment, and response to therapy. The second is to increase awareness that CNO can involve the petrous temporal bone with the hope it will aid in diagnostic clarity for challenging cases. Methods Cases of patients diagnosed with CNO between June 2002-May 2022 at The Hospital for Sick Children were identified by searching Bialogics and the Electronic Medical Record Epic. Charts were searched for the term “skull” to identify cases affecting the skull. To obtain records prior to 2018 we ran a word search of pertinent synonyms to identify cases of CNO involving the temporal bone in the ISYS imagining system. Research Ethics Board approval was obtained. Results Three cases of CNO affecting the petrous temporal bone, were identified (Figure 1). All had known CNO peripheral lesions. They ranged in age from 2-10 years old and were female. Two patients had 7th cranial nerve involvement and hearing loss. All patients were treated with a non-steroidal anti-inflammatory drug (NSAID) and 2 patients with hearing loss received anti-TNF therapy (adalimumab) and responded well with resolution of hearing loss in 1 case and residual mild to moderate conductive hearing loss in another. These cases are unique as they involve the skull, a less affected CNO site.[1,2] It typically affects metaphysis and epiphyses of the long bones, vertebral bodies, and the clavicle. Axial skeletal involvement is less prevalent (61%) compared to appendicular skeleton involvement (75%).[2] With 1% of patients presenting with skull lesions.[1,2] It is unknown why CNO rarely affects the skull. Theories include CNO tends to affect the metaphysis and epiphyses of the long bones which the skull does not have. Another is there is increased metabolic activity at the epiphysis with chondrocyte maturation which could result in increased propensity of immune dysregulation and inflammatory lesions.[3] Conclusion CNO typically affects the metaphysis of the long bone but can affect any bone in the body, including the temporal petrous bone of the skull. It is important to consider CNO on the differential in patients who present with cranial nerve abnormalities, facial nerve palsy, hearing loss, and those with presumed infectious osteomyelitis. [1.] Ferrara G. Clin Exp Rheumatol 2020;38(2):366-9. [2.] Borzutzky A. Pediatrics 2012;130(5):e1190-7. [3.] Shapiro IM. 2007;40(3):561-7. Best Abstract on Pediatric Research by Early Career Faculty Award

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