CNO syndrome M86.9-

CNO (CNO is the acronym for "chronic non-bacterial osteomyelitis") is an autoinflammatory, non-bacterial bone disease with a wide spectrum of clinical manifestations, ranging from unifocal to multifocal lesions.

Chronic recurrent multifocal osteomyelitis(CRMO) on the other hand, is a severe form of CNO, usually characterized by symmetric, inflammatory bone lesions, and their waxing and waning manifestations.

The pathophysiology of CNO is unclear. Imbalanced cytokine expression and increased inflammasome activation in monocytes from CNO patients suggest a pro-inflammatory phenotype contributing to (non-bacterial) bone inflammation.

CNO/CRMO can affect all age groups, although the pediatric population is most commonly affected.

S.u. CRMO syndrome

In the absence of validated diagnostic criteria, CNO/CRMO remains a diagnosis of exclusion. Bone biopsy does not reveal a specific clinical picture, but may be necessary in unifocal or atypical cases to differentiate the disease from malignancy or infectious osteomyelitis.

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6. Zhao DY et al (2021) Chronic nonbacterial osteomyelitis (CNO) and chronic recurrent multifocal osteomyelitis (CRMO). J Transl Autoimmune 4:100095.