Background One of the most important knowledge of rheumatoid arthritis (RA) landmarks has been evidence that an early and vigorous treatment interferes with the progression and its physical consequences. That is why the early diagnosis has become essential. Today it is considered that the diagnosis must be made within the first 3 months of the onset of the disease, the period in which aggressive treatment should be started before the anatomical damage appears (“The Window oportunity”). The term of “indefinite arthritis” includes patients with different clinical ways of expression, shaped self-limiten arthralgia or arthritis of such low activity forms that when evaluated by the rheumatologis no notes about, so it is raeallity difficult the early manegement of this patients. There are a second group of patients with arthritis observable when assessed do not meet the classification criteria for RA, terming these forms as “undifferentiated arthritis” (UA). A third group of patients to be evaluated who meet the diagnostic criteria for RA are defined as “recent onset rheumatoid arthritis” RRA”. Finally, there are a group of patient who are referred with positive laboratory tests without clinical disease criteria.

Objectives 1) To evaluate UA prognostics factors in patients with UA that allow us to predict evolve to defined RA. 2) Analysis of other clinical characteristics predictive of progression to RA.

Methods Descriptive observational study of a cohort of patients who, after a first clinical evaluation are diagnosed with UA, from 2005 to 2015, presenting arthritis in one or more joints lasting less than one year of evolution and not meet 87 ACR diagnostic criteria for RA. Of the patients evaluated at that time, 200 were diagnosed with UA and subsequently followed for more than 3 years. Were analyzed baseline and diagnosis characteristics for each patient

Results Of the 200 patients diagnosed with (UA), 72 were women (52.2%) with a mean age of 48.44 (17–87) years. During the 12-month follow-up, 40 (20%) evolved AR, 52 (26%) a palindromic rheumatism, 53 (26.5%) and 52 to other rheumatic disease (26%) remained as undifferentiated. Of the group of patients who evolved RRA, 53.6% were women, with an average age of 51.7 (18–82) years. Introducing a form of polyarticular onset in 27 (67.5%), small and medium joints affected 22 (55%), symmetrical involvement 36 (90%) and morning stiffness>1 hour 20 (50%). 75% were FR+, OR =2.49 (95% CI =2.11 to 8.13) and 78,5% were ACPCC +, while it was negative in patients with UA remained as an OR =9.77 (95% CI 4.18 to 22.8). At 3 years of follow-up only 5.1% remained as undifferenciated forms, 24.8% as palindromic forms.

Conclusions For early diagnosis, it is essential to identify patients with UA to develop an AR. A quarter of the patients analyzed in our study diagnosed with UA, evolved AR. Patients evolved AR debuted in more than half of the cases with a predominance of polyarticular involvement and medium and small joints affected. The presence of RF and ACPA are predictors of evolution AR, being the latter the most relevant.

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Disclosure of Interest None declared