Title: Role of Synovial Biopsy in Diagnosis of Crystal Arthropathies

Background/Purpose: Diagnosis of crystal arthropathies (CAs) can be challenging. Advances in arthroscopy and ultrasound guided procedures have enhanced the ease and availability of synovial biopsy as a diagnostic test for rheumatologists, leading us to examine the role of synovial biopsy in CAs.

Methods: We performed word searches on synovial biopsies in the pathology database of a tertiary referral medical center between 1988 and 2015 and identified two groups. (1) A “clinical” group where CA was clinically suspected and listed as a primary or secondary indication for biopsy (with biopsy subsequently either positive or negative for CA); this would be typical of biopsy requests for CA originating from a rheumatology setting. (2) An “incidental” group, where a CA was identified on biopsies submitted from diagnostic and therapeutic procedures without a preoperative suspicion of CA. We reviewed electronic medical records of these cases to extract clinical details.

Results: Of 2786 synovial biopsies reported during the study period, 98 cases were selected for further study (Fig. 1). The mean age was 55 +/-16 years and 45% were female. Biopsy reports in the two groups are summarized in Fig. 1. On restricting analysis of the “clinical” group to only biopsies with CA as the primary clinical suspicion (n=31), the proportion of CA positive biopsies rose to 16% for gout, 13% for CPPD, 10% for unspecified crystal, with 39% overall positive for any crystal, while 22% had an alternate diagnosis and 39% were non-diagnostic. Absolute alcohol was the fixative used for 81% of the specimens in the “clinical” group. Seven of the 33 “incidental” positive biopsies were mass lesions suspected to be neoplastic, but diagnosed by biopsy as gout (n=4) or CPP (n=3). Clinical characteristics of patients from either group with a biopsy diagnosis of gout and CPP respectively were compared with the “clinical” patients negative for CA. (Table 1) Synovial fluid findings could not be analyzed due to a paucity of data.

Conclusion: Synovial biopsy is useful in the diagnosis of CAs, (a) yielding a diagnosis that can influence management in 61% of cases, (b) detecting a CA in 39%, and (c) identifying a specific CA in 29%, when CA is the primary indication for biopsy. Biopsy-positive gout is associated with the presence of bone cysts, while biopsy-positive CPP is associated with older age, monoarticular disease, chondrocalcinosis and bone cysts. An unexpected diagnosis of CA or crystal deposition occurs in 1% of synovial biopsies from procedures with no prior suspicion of a CA, including occasional mass lesions clinically mimicking a neoplasm.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/role-of-synovial-biopsy-in-diagnosis-of-crystal-arthropathies/