Background/Purpose: Gout flares are the most common manifestations of gout. Awareness of possible disease presentations beyond the traditionally recognized podagra is essential for accurate and early diagnosis. Gout flares sparing the first metatarsophalangeal (MTP1) joint may be prone to misdiagnosis as physicians may not consider other patterns of joint involvement in a gout flare. We therefore examined gout flare joint patterns in two large gout cohorts.

Methods: We used data from the Boston Online Gout Study (BOGS), a longitudinal internet-based case-crossover study recruited from the community in the US, and the Study for Updated Gout Classification Criteria (SUGAR), a single time-point international cohort of patients presenting to Rheumatology clinics, to identify patterns of joint involvement and their frequency in gout flares through latent class analysis. In BOGS, we analyzed the joints affected in the first recurrent gout flare reported during the study, while in SUGAR, we analyzed the joints affected at study enrollment. Latent class models with different numbers of classes (patterns) were evaluated, with the optimal number determined by statistical parameters, mean posterior probability of class membership, and clinical judgment.

Results: BOGS included 724 participants, 78% men, mean age 54 years, with mean gout duration of 8 years. SUGAR included 509 subjects with crystal-proven gout, 86% men, mean age 60 years and mean gout duration of 6 years. The optimal model for both studies included four patterns of predominant joint involvement, with mean posterior probability of class membership being ≥79%, indicating a good fit of the group trajectories model. In BOGS, the most common pattern was involvement of lower limb joints (including MTP1), with a prevalence of 49.8%, followed by MTP1 monoarthritis (32.5%), upper limb joint involvement (14.5%), and polyarticular flare (3.1%). Similar patterns were identified in SUGAR, with MTP1 monoarthritis (39.4%) and knee/ankle involvement (37.1%) being the most common, followed by upper limb joint pattern (14.8%) and polyarticular flare (8.6%). (Table) Of note, 43.7% and 64.2% of subjects in BOGS and SUGAR, respectively, had a gout flare in joint(s) other than the MTP1. Upper limb and polyarticular flares appeared to be associated with longer disease duration.

Conclusion: We identified similar patterns of joint involvement in two large cohorts of gout patients from both the community and Rheumatology practices. While MTP1 monoarthritis was common, other lower extremity joint patterns were also common. These findings are important to increase awareness of different gout flare presentations among health care providers to improve gout flare diagnosis, including a not uncommon pattern of upper limb involvement. Importantly, lack of MTP1 involvement does not rule out the possibility of a gout flare, especially among patients with longer disease duration.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/patterns-of-joint-involvement-in-gout-flares/