Clinical presentation of early arthritis is frequently as undifferentiated arthritis with various onset (mono, oligo and polyarthritis) and course of the disease, with the duration of the symptoms Ł3 months. Establishing the proper diagnosis in these patients is a difficult task. The aim of this study was to:
1) estimate the proportion of patients with undifferentiated arthritis who can be classified as having rheumatoid arthritis or other rheumatic diseases according to recommended classification criteria,
2) estimate the duration of the disease from the first clinical symptoms to establishing the diagnosis.
In a group of 78 patients with undifferentiated early arthritis, clinical evaluation, laboratory examinations, disease activity parameters (ESR, CRP), DAS 28 and HAQ-DI were performed. In all patients, the fulfilment of ACR 1987 and ARA 1961 classification criteria for rheumatoid arthritis were estimated. ACR 1987 classification criteria were fulfilled in 19% of patients with oligoarthritis and 49% with polyarthritis. Definite ARA 1961 classification criteria were fulfilled in 11% of patients with oligoarthritis and in 57% with polyarthritis. Probable ARA 1961 classification criteria were fulfilled in 32% of patients with oligoarthritis and in 33% with polyarthritis. None of the patients with monoarthritis fulfilled the mentioned criteria. The mean time from the first clinical symptoms of the disease to establishing the diagnosis was 9 months. The results of these studies indicate the need for new rheumatoid arthritis classification criteria including early stage of the disease.