Autoinflammatory bone disorders.

Autoinflammatory bone disorders are characterized by chronic non-infectious osteomyelitis and inflammation-induced bone resorption and result from aberrant activation of the innate immune system. Sporadic chronic non-bacterial osteomyelitis (CNO) is the most common disease subtype. The clinical picture is highly variable and the exact underlying pathophysiology remains to be determined. Recently, novel insights in the pathophysiology of sterile bone inflammation have been gathered by analyzing patients with rare, monogenic inflammatory diseases. In this overview CNO and Majeed syndrome, cherubism, hypophosphatasia and primary hypertrophic osteoarthropathy will be discussed. For the latter four disorders, a genetic cause affecting bone metabolism and leading to chronic bone inflammation has been described. The exact pathophysiology of CNO remains to be determined. Insights from monogenic autoinflammatory bone diseases and the identification of distinct inflammatory pathways may help to understand the pathogenesis of bone inflammation and inflammation-induced bone resorption in more common diseases.