To determine how experts would classify 10 early-arthritis cases (7 atypical) and to study discrepancies in diagnoses relative to ACR criteria for rheumatoid arthritis (RA) or ESSG criteria for spondyloarthropathy (SpA).
Ten real cases (5 met ACR criteria for RA, 6 ESSG criteria for SpA, 3 both and 2 neither) followed for 28.5 +/- 4.8 months were sent as paper cases to 20 international and 12 French experts. Each expert selected a diagnosis among 8 possible choices and rated it on a 0-10 confidence scale. For each case, 3 analog scales (0-100 mm) were used to indicate the probability of RA, SpA or undifferentiated arthritis (UA).
Experts often disagreed about diagnoses (up to 5 different diagnoses for a given case, with a mean of 3.9 per case). Similarly, expert opinions on probabilities for RA and SpA differed widely, with great overlap between confidence for RA, SpA and UA. Fulfilment of ACR or ESSG criteria was poorly related to the experts' diagnosis and evaluation of probabilities for RA and SpA. However, UA was a relatively infrequent choice (19%).
There was no general consensus about the nosology of early RA and SpA. Classification of atypical early arthritis was not resolved by currently available criteria for RA and SpA. This may have implications for therapy in early disease.