Chlamydia reactive arthritis most commonly presents as an asymmetric oligoarthritis with lower extremity predominance¹. It can have a poor prognosis due to reinfection, variable clinical manifestations, and overlap with other common inflammatory arthropathies. Although magnetic resonance imaging (MRI) is often used to evaluate joint effusions, the average wait times have exceeded two to four weeks with costs ranging between $300-$5,000 dollars². Point-of-care ultrasound (POCUS) can be used as an efficient diagnostic resource while navigating through the list of differential diagnoses³.

A 45-year-old man presented with 3-weeks of atraumatic left ankle pain with warmth, erythema, and edema that his primary care physician treated empirically as gout.  He was referred to Rheumatology due to a lack of improvement with NSAIDs and colchicine.

Initial POCUS revealed peroneus tenosynovitis, double-contour sign, and a heteroechoic mass suspicious for a tophus (figure 1a). X-rays and MRI demonstrated similar findings; however, the synovial fluid analysis showed a noninflammatory cell count, no crystals, and a negative culture.  He was treated with local steroid injection for presumed spondyloarthritis vs. persistent gout.

Within two weeks, the swelling returned.  The patient reported dysuria, which prompted further testing notably for Chlamydia and HLA-B27.  Following treatment with doxycycline, a repeat ultrasound at a 2-month follow-up showed resolution (figure 2a/2b).