Background/Purpose: Synovial biopsies have an important role in the diagnostic evaluation of patients with undifferentiated inflammatory arthritis (UIA) whose clinical examination and blood and synovial fluid testing do not yield a diagnosis. Several methods are used to perform synovial biopsies, including arthroscopic surgery, fluoroscopic guided and blind needle synovial biopsies. In recent years, ultrasound (US) technology has progressed significantly with improved image resolution, musculoskeletal US expertise, and feasibility of US-guided synovial needle biopsies (USGSB). We studied the safety, tolerability, and utility of USGSB in patients with UIA and rheumatoid arthritis (RA).

Methods: Between 2016-2019, we identified all patients referred for USGSB to a single academic medical center. 2 groups of patients underwent this procedure, patients with UIA and those with RA with significant synovitis despite therapy. Chart review was performed to identify clinical characteristics of these patients. For each patient, tissue samples were sent to pathology in formalin for standard histologic evaluation, methanol for anhydrous histologic evaluation, and sterile containers for typical and atypical cultures.

Results: A total of 25 patients were referred for USGSB. There were 18 patients (72%) with UIA and 7 (28%) with RA. All patients presented with inflammatory arthritis > 6 weeks duration. 8 patients had monoarthritis, 4 with oligoarthritis and 13 with polyarthritis. Of the 13 patients with polyarthritis, 7 were previously diagnosed with RA. Demographic and clinical characteristics of patients are shown in Table 1. The results of the biopsies are detailed in Table 2.

Of the 25 USGSB performed, 20 biopsies (80%) retrieved synovial lining cells and thus passed quality control. 5 had no synovial lining cells and therefore were deemed inadequate. Overall, 7 of 25 biopsies showed normal synovium (including 4 RA) and 6 demonstrated chronic lymphocytic inflammation. Among the 6 biopsies with chronic lymphocytic inflammation, 2 were already diagnosed with RA and had been treated with biologic therapy. Among the 4 RA patients with normal synovium on USGSB, one was treated with chronic low dose prednisone and all were on biologic therapy.

The use of USGSB resulted in a definitive diagnosis in 13 out of 14 patients with UIA, while 1 patient remained with the diagnosis of UIA. Among the 13 patients with a definitive diagnosis, 11 of the synovial biopsies helped to achieve a final diagnosis. 2 patients had acute neutrophilic predominant inflammation on USGSB and were treated with empiric antibiotics for presumed infectious arthritis, although cultures were subsequently negative. One patient had septic arthritis. Three patients had CPPD crystals consistent with pseudo gout. One patient had PVNS. The detail of final diagnoses can be seen in Table 3.

All patients tolerated the USGSB procedure well without any complications such as bleeding or infection. Three reported increased  stiffness in the biopsied joint, which was resolved over several days.

Conclusion: USGSB is a well-tolerated procedure. Given the minimally invasive nature of the technique, it can be a useful tool to aid in the diagnosis of challenging cases of inflammatory arthritis.

UIA table 1

UIA table 2

UIA table 3

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ultrasound-guided-synovial-biopsies-safely-aid-in-the-assessment-of-inflammatory-arthritis/