Diagnostic value of 18-F fluorodeoxyglucose PET/CT and bone scan in Schnitzler syndrome

Introduction: Schnitzler syndrome is an auto-inflammatory disease defined by chronic urticarial eruption and monoclonal gammopathy. ¹⁸F fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) is often performed, but its utility in Schnitzler syndrome has not been specifically investigated. The aim of this study was to determine whether PET/CT is informative in the diagnosis and follow-up of Schnitzler syndrome relative to other imaging techniques, including bone scans.Patients and methods: Patients of this study were selected from the French cohort established by Néel et al. All patients with a diagnosis of Schnitzler syndrome (according to Strasbourg's and Lipsker's criteria) who had at least one PET/CT were included. Data were collected from medical records. PET/CT scans were all reviewed by a nuclear physician blinded to the clinical and imaging data.Results: Ten patients underwent at least one PET/CT scan and all had at least one ^99mTechnetium bone scan during their follow-up. The most frequent PET/CT abnormalities were diffuse bone-marrow and/or increased femoral fluorodeoxyglucose uptake, but they did not correlate with disease activity. Conversely, bone-scan abnormalities, including mainly increased radiotracer uptake in long bones, appeared to strongly correlate with Schnitzler syndrome activity.Discussion: PET/CT does not appear to be useful for the diagnosis and follow-up of Schnitzler syndrome. However, bone scans appear to be more sensitive for diagnosis and may correlate with clinical activity. Bone scans may be well positioned to distinguish Schnitzler syndrome relapse from other aetiologies of bone, joint, or muscle pain.Conclusion: Bone scans may be favoured over PET/CT in Schnitzler syndrome.