Chronic non-bacterial osteomyelitis (CNO) is an inflammatory bone disease, usually diagnosed in childhood. It is characterized by the presence of multifocal or unifocal osteolytic lesions that can cause bone pain and soft tissue swelling. CNO is known to have soft tissue involvement. However, soft tissue involvement large enough to give the appearance of a mass is rare. This article discusses a case of CNO with a mass-like appearance that involved soft tissue and spontaneously regressed, as well as presents CNO cases with soft tissue involvement and conducts a literature review on this subject. Our investigation revealed that edema and synovitis were the most frequently observed soft tissue involvements in association with CNO. Moreover, we also encountered myositis, a mass-like appearance, neuritis, and polyserositis within the surrounding muscles. Although, it is well known that bone inflammation tends to regress spontaneously in CNO patients which reflects the autoinflammatory nature of the disease, there is no such patient whose soft tissue involvement which has mass like appearance improved spontaneously. Therefore, we aimed to emphasize the clinical progress which can be easily underdiagnosed of CNO patients by the clinicians by presenting unique features of our patient and our detailed literature review.
