Pos0487 disentangling heterogeneity in contemporary undifferentiated arthritis – a large cohort study using latent class analysis

Background Undifferentiated arthritis (UA) is considered to be heterogenous and consists of subgroups, this notion is affirmed by differences in disease course, varying from spontaneous resolution of arthritis to RA-development. Objectives We aimed to identify homogeneous subgroups within UA based on a combination of clinical features and thereafter to relate these to the outcomes spontaneous resolution and RA-development. These outcomes can only be studied in UA-patients in which DMARD-treatment does not influence the natural disease course; these cohorts are scarce. Methods We studied ACPA-negative UA-patients, defined as not-fulfilling 1987-/2010-RA-criteria nor having an alternate diagnosis, consecutively included in the Leiden Early Arthritis Clinic between 1993-2006, when early DMARD-treatment in UA was infrequent. Latent Class Analysis was used to identify subgroups based on a combination of clinical features (e.g. symptom characteristics, physical examination, laboratory tests). Within these subgroups, test-characteristics were assessed for spontaneous-resolution of arthritis (defined as spontaneous resolution of arthritis without DMARD-treatment) and RA-development within 1 year. Results 310 consecutive UA-patients were studied. Five classes were identified: location and number of swollen joints were most distinguishing. Classes were characterized by: 1) polyarthritis, often symmetric 2) oligoarthritis, frequently with subacute onset, 3) wrist-monoarthritis, often with subacute onset, increased BMI and without morning stiffness, 4) small-joint monoarthritis, often without increased acute phase reactants, and 5) large-joint monoarthritis, often with subacute onset. Studying the classes in relation to the outcomes revealed that the majority of patients without spontaneous resolution were not included in the classes characterised by monoarthritis (specificity >90%). In addition, patients who developed RA were infrequent in the monoarthritis classes (sensitivity <7%). Conclusion Using a data-driven unsupervised approach, five subgroups within contemporary UA were identified. These subgroups have differences in the natural course of disease. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests None Declared.