Chronicnon-bacterial osteomyelitis (CNO) is an inflammatory bone disorder of yet unknown origin. The clinical spectrum ranges from relatively benign, self-limiting, mono-focal symptoms to destructive, multi-focal involvement (known as chronic recurrent multifocal osteomyelitis, CRMO). Secondary to the absence of high-titer autoantibodies and autoreactive T lymphocytes, CNO was classified as an autoinflammatory disorder. The diagnosis is based on the clinical picture, the exclusion of differential diagnoses (including infections and malignancies), and radiographic findings. Treatment options are empiric, including NSAIDs as first line therapy, and steroids, bisphosphonates, or biologicals in more treatment resistant cases.
To date, the etiopathology of CNO remains to be elucidated. Linkage analyses point to a susceptibility locus on chromosome 18q. However, conclusive evidence is lacking. A rare syndromal form of CNO, referred to as Majeed syndrome, has been linked to mutations in the LPIN2 gene on chromosome 18p. Further autoinflammatory syndromes, namely deficiency of IL-1 receptor antagonist (DIRA; mutations in IL1RN) and pyogenic arthritis, pyoderma gangrenosum and acne (PAPA; mutations in CD2BP1 gene), share bone inflammation with CNO, however presenting with a more severe clinical picture.
We will discuss 1) animal models, mimicking the phenotype of CRMO, 2) how genetic and immunological findings in related disorders may contribute to a better understanding of the pathophysiology of bone inflammation in CNO, and 3) most recent findings, indicating that monocytes from CNO patients fail to produce IL-10, resulting in a disrupted balance between pro- and anti-inflammatory cytokines.
Disclosure of Interest None Declared
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