Prospective diagnostic performance of PET/CT using the novel fibroblast imaging tracer 18F-AlF-FAPI-74 versus standard of care 18F-FDG in inflammatory disorders.

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• A. General: - Voluntary written informed consent must be obtained prior to any screening procedures. - Subject is aged over 18 years, M/F. - Female subjects should be (a) post-menopausal, or (b) surgically sterile, or (c) using effective contraceptive with negative pregnancy test. B. FUO - Patient underwent a [18F]FDG PET/CT or is planned to have one in the following 2 weeks. - Subjects should fulfil the criteria for classic FUO or IUO o FUO  An illness of more than 3 weeks’ duration,  Temperature exceeding 38.3°C on > 3 occasions,  Diagnosis uncertain despite appropriate first-line investigations. o IUO  An illness of more than 3 weeks’ duration,  Temperature not exceeding 38.3°C on > 3 occasions,  Raised inflammatory markers (C-reactive protein > 30mg/dL) on > 3 occasions,  Diagnosis uncertain despite appropriate first-line investigations. C. IgG4 - Patient underwent a [18F]FDG PET/CT or is planned to have one in the following 2 weeks. - High clinical suspicion of IgG4-RD by an experienced clinician of Internal Medicine, based on anamnesis, physical examination, first-line investigations and blood tests. - Patients with a new diagnosis of IgG4-RD on histopathology and need for further assessment of disease extent with PET/CT, - Relapse of diagnosed IgG4-RD on histopathology, according to the 2019 American College of Rheumatology/European League Against Rheumatism Criteria for IgG4-related Disease, with moderate to high disease activity. D. AxSpa - For the inflammatory back pain cohort: o High clinical suspicion of axial spondyloarthropahy according to an experienced rheumatology (based on inflammary back pain > 3 months, insidious onset, morning stifness, improvement with exercise and worsening in rest, pain worse at night, age at onset <45 years of age, imaging findings). o Patient has persisting inflammatory back pain after 2 different types of NSAID’s (tried for over 2-4 weeks), and is therefore eligible for biological DMARDS therapy. - For the mechanical back pain cohort: o Lower back pain of mechanical origin (discus, fact joint, …), confirmed by MRI findings of the lumbar spine. o Not caused by trauma. E. NMD a. Inflammatory neuromuscular group • Diagnosis of an inflammatory disease, particularly: o Sporadic inclusion body myositis (sIBM), or o Idiopathic inflammatory myopathies (IIM) b. Neuromuscular diseases control group • Diagnosis of one of the following acquired or hereditary neuromuscular disorders: o Glycogen storage myopathy type 2 (GSD2) o Limb-girdle muscular dystrophies (LGMD) o Becker muscular dystrophy (BMD) o Facioscapulohumeral muscular dystrophy (FSHD) o Oculopharyngeal muscular dystrophy (OPMD) o Myotonic dystrophy type 1 (DM1) o Therapy-refractory myasthenia gravis (MG) c. Healthy Control group • No known ongoing inflammatory, neuromuscular, oncological or metabolic disorders.