A remarkable case of active spondyloarthritis

A 25 year-old male patient presented with a 2-week history of inflammatory back pain and right heel ache. He was known to suffer from undifferentiated spondyloarthritis, with lumbar spondylitis and peripheral enthesitis. He was off therapy, but had been previously treated with biologics. Physical examination revealed a negative Patrick's test, tenderness at the insertion of the right Achilles tendon to the calcaneus, and tenderness upon palpation of the lumbar spinous processes. Ultrasound showed signs of peripheral enthesitis, and magnetic resonance imaging (MRI) scan displayed active lumbar interspinous bursitis (Figure 1A, arrows), with no signs of sacroiliitis. No close approximation of the spinous processes was present, ruling out Baastrup disease. Known erosions were also seen at 2 lumbar vertebral bodies, L1 and L5 (Figure 1B, arrows). The concomitant interspinous bursitis and peripheral enthesitis were considered signs of active spondyloarthritis. Treatment with etoricoxib was started, with a remarkable clinical improvement. The renewal of targeted therapy was discussed with the patient. Active spondyloarthritis may present as bursitis.1 In fact, bursal tissue has been suggested to contribute to the enthesis complex,2 implying a link between bursitis and enthesopathy.3 While interspinous bursitis has been well-described in polymyalgia rheumatica,4 to the best of our knowledge, this is the first report of interspinous bursitis as a manifestation of active axial spondyloarthritis. The authors have no conflict of interests to declare.