Fever of unknown origin (FUO) and chronic inflammatory syndrome could be seen in many affections. The diagnostic process is still a challenge and could not be specified yet after several clinical studies performed by trained teams using two levels diagnostic procedures. For this reason, the diagnosis involves many additional and expensive tests such as computed tomography (CT scan), scintigraphic imaging, endoscopy, biopsy. There is no evidence-based recommendation for the diagnostic work-up of FUO or chronic inflammatory syndrome. Positron emission tomography with 2-[18F] fluoro-2-deoxy-D-glucose combined with CT scan (FDG-PET/CT) is widely used in malignant diseases and seems to be promising for the diagnosis of inflammatory disorders. Its role has not been yet clearly defined in the investigation of FUO and chronic inflammatory syndrome.

All patients with FUO and chronic inflammatory syndrome will undergo FDG-PET/CT and conventional morphologic imaging modalities. Results of these two diagnostic procedures in identifying diagnostic clues will be compared.

We assume FDG-PET/CT could be safer and more helpful to reach early final diagnosis in patients with FUO and chronic inflammatory syndrome than conventional morphologic imaging modalities

Inclusion Criteria:

• Patient with FUO criteria:

Fever since 3 weeks, Temperature > 38.3°C, No diagnostic after 3 days of hospitalization.

• Patient with periodic fever criteria:

Fever with criteria like FUO, Fever-free intervals, and apparent remission of the underlying disease, At least 3 febrile episodes.

• Inflammatory syndrome without any clinical sign, Important inflammatory syndrome: Erythrocyte sedimentation rate ≥ 50 at the first hour, and elevation of at least one another inflammatory parameter (haptoglobin, orosomucoïd, fibrinogen or C-reactive protein), Evolution since more than 3 weeks, No diagnostic orientation after clinical examination and history-taking, No diagnostic clue after 3 days of hospitalisation.
• Oral informed consent obtained.

Exclusion Criteria:

• Demented patient or unable to receive information on the protocol and to give informed consent.
• Pregnant women, or without contraception.
• Contraindication to iodine examination, gallium scintigraphy or 18FDG TEP-scan.
• Immunodeficient patient.
• Know HIV infection, neutropenic patient and nosocomial fever.