Imaging findings in 22 cases of Schnitzler syndrome: characteristic para-articular osteosclerosis, and the hot knees sign differential diagnosis

Schnitzler syndrome is characterized by chronic urticaria, monoclonal gammopathy, and a risk of developing lymphoproliferative disorders. Patients frequently present with bone pain, fever, arthralgia, and lymphadenopathy. The purpose of this study is to retrospectively review and evaluate potentially attributable imaging abnormalities in a series of patients with clinically diagnosed Schnitzler syndrome. Clinical and pathological chart review identified 22 patients meeting Strasbourg criteria for Schnitzler syndrome. Imaging of these patients was retrospectively reviewed by a musculoskeletal radiologist and a radiology fellow to determine and characterize significant positive findings that could potentially be attributed to their primary disease process. Evidence of abnormal bone remodeling was present in 64 % (14/22) of patients with 40 bone abnormalities. Lesions were predominantly or entirely sclerotic and most commonly involved the distal femora (n = 11), proximal tibiae (nine), and innominate bones (six). Patterns of involvement were variable, but typically eccentrically intramedullary, cortical, and juxta-articular. Skeletal surveys and targeted radiographs identified only 37 % (10/27) of abnormal bones subsequently positive by additional modalities. PET and bone scans were all positive in patients with bone sclerosis (13/13 and 17/17 bone sites, respectively). Schnitzler syndrome often presents with characteristic osteosclerosis, most commonly around the knees and in the pelvis. In patients with a suggestive clinical history, the radiologist could direct an appropriate imaging strategy or might to be the first to suggest the diagnosis. Bone scan may be the most appropriate initial screening tool in suspected cases.