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Objective: Monoarticular presentation of rheumatoid arthritis is infrequent and has been previously reported to involve large joints such as the hip and knee joints. Here we report a case series of four patients presenting to the University of Michigan in 2015 with monoarticular rheumatoid arthritis, one with small and three with large joint involvement. Material and Methods: In total, four patients with monoarticular rheumatoid arthritis were treated in the Division of Rheumatology, University of Michigan. All the patients were retrospectively reviewed with permission from our Institutional Review Board; informed consent was provided by the patients for enrollment in a clinical trial for patients with rheumatoid arthritis. All the patients were assessed using the 2010 ACR/EULAR classification criteria for rheumatoid arthritis. Results: All the patients presented with monoarthritis; three patients had large joint involvement and one had small joint involvement. Serologies were positive, with each patient having positive Anti-cyclic citrullinated peptide (anti-CCP) antibodies, two patients having a positive rheumatoid factor, three patients having elevated CRP levels, and one patient having positive ESR. All patients met the criteria of the duration of symptoms being at least 6 weeks. The findings of imaging, although not a part of the criteria, were consistent with active rheumatoid arthritis in all the patients. Conclusion: While the 2010 ACR/EULAR classification criteria are the most sensitive criteria for diagnosing RA to date, the exclusion of these cases of monoarthritis demonstrates that further specificity can still be achieved for diagnosing these types of patients as early as possible using the current guidelines. Further, we suggest the inclusion of an imaging measure added to the inclusion criteria to further increase the yield in establishing diagnosis of rheumatoid arthritis in the current reported patient population. [ABSTRACT FROM AUTHOR]

Lipoma arborescens is a rare and benign intra-articular lesion of unknown etiology; it is characterized by synovial villous proliferation and sub-synovial connective tissue replacement by mature fatty tissue. It is part of the differential diagnosis in patients with an articulation affected by a slow, progressive, and chronically inflamed affection. We report primary knee involvement in a patient without significant articulate antecedents. Lipoma arborescens was diagnosed after knee magnetic resonance imaging and was confirmed by an anatomopathological study of the surgical specimen. [ABSTRACT FROM AUTHOR]