Abstract
The classic form of fever of unknown origin (FUO) in adults is defined as a temperature > 38,3°C on several occasions over a period > 3 weeks, and diagnostic uncertain after 1 week of inpatient investigation or ≥ 3 outpatient visits. The analysis of FUO includes diagnostic groups and definite diagnoses.
Rheumatic diseases are evaluated as a separate group or in a larger group of non-infectious inflammations; they represent about 25% of all causes of FUO, and take 2nd or 3rd place after the group of infections and/or persistently unexplicated FUO. In rheumatic patients < 40 y/o, the most frequent diagnoses are systemic lupus erythematosus, adult-onset of Still disease and regionally also hereditary mediteranean fever, in 50+ y/o patients with giant cell arteritis; FUO manifestation in ANCA+ vasculitides may be present at any time.
The difficult aspect of diagnostic process in FUO is detection of potenntially diagnostic clues (PDCs) defined as all localising signs, symptoms, and abnormalities potentially pointing toward a diagnosis. Especially in this connection the rheumatologist has an important and specific role in management of FUO.