PO:05:066 | Atypical diagnosis and manifestation of spondyloarthritis: a case report

Adele Del Giudice¹, Filippo Crescentini², Giorgia Citriniti², Luca Cimino^1|3, Carlo Salvarani^1|2 | ¹Department of Rheumatology, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario A. Gemelli IRCCS, Roma, Italy; ²Department of Medicine, University of Melbourne at St Vincent's Hospital Melbourne, Australia; ³Department of Rheumatology, Division of Medicine, University College, London, UK

Background. The aim of this case report is to illustrate how the initially most likely diagnosis is not always the correct one.

Case report. A 57-year-old woman, with an unremarkable past medical history, presented to our attention following ophthalmologic referral after a first episode of acute non-granulomatous unilateral anterior uveitis, associated with arthralgias involving the shoulder and knee girdles, and prolonged morning stiffness (90 minutes). She denied previous episodes of arthritis, RS3PE, headache, transient visual loss, diplopia, scalp dysesthesias, enthesitis, dactylitis, or inflammatory low back pain. There was no personal or family history of psoriasis or inflammatory bowel disease. Based on laboratory findings (elevated nonspecific inflammatory markers), clinical presentation (EUL 3/3 with painful arc and prolonged stiffness), and ultrasound evidence (bilateral subacromial–subdeltoid bursitis with long head biceps tenosynovitis, knee and shoulder synovitis), a diagnosis of polymyalgia rheumatica (PMR) was initially made. Treatment with tapering prednisone (starting at 12.5 mg/day) was initiated, with an excellent initial response. At subsequent visits, the patient reported recurrence of symptoms at prednisone doses below 7.5 mg/day, leading to the addition of methotrexate 15 mg/week as a corticosteroid-sparing agent. Due to poor clinical response and frequent need for NSAIDs to control symptoms, a repeat joint ultrasound was performed, confirming previous findings and revealing polyenthesitis (involving subscapularis, supraspinatus, and distal patellar tendons) with bilateral microerosions. Laboratory testing showed positivity for HLA-B27. In light of these new findings, the diagnosis was revised to HLA-B27–positive peripheral spondyloarthritis with a polymyalgia-like onset, and anti–TNFα therapy (adalimumab) was initiated. Over the following months, progressive loss of drug efficacy was observed, with new-onset inflammatory pain involving the cervical spine and anterior chest wall, exacerbated by inspiration. MRI revealed bilateral sternoclavicular synovitis and inflammatory involvement of the manubriosternal junction and interspinous ligament from C7 to D1. Based on these findings, the diagnosis was further revised to combined axial and peripheral HLA-B27–positive spondyloarthritis, complicated by acute non-granulomatous anterior uveitis. The patient was switched to a second anti–TNFα agent (certolizumab), achieving good clinical response and stable remission.

Conclusions. This case highlights the importance of a broad and dynamic diagnostic approach, even in the presence of clinical pictures apparently consistent with common conditions such as PMR. The polymyalgia-like onset represented a diagnostic challenge, which was overcome only through close follow-up, targeted joint imaging, and immunogenetic assessment. Spondyloarthritis may present with atypical phenotypes, mimicking other rheumatologic diseases. Therefore, meticulous attention to clinical and instrumental details is essential to avoid diagnostic delays and ensure timely initiation of appropriate treatment.