Rheumatoid arthritis (RA) and spondyloarthritis(SpA) are chronic inflammatory disorders with unique symptoms and pathologies. Misclassification of these two entities is prevalent due to overlapping clinical features and the presence of typical symptoms for both disorders. Rheumatoid nodules are one of the most common extra articular manifestations in rheumatoid arthritis, usually associated with severe disease activity. Herein, we describe a case of rheumatoid arthritis with bilateral sacroiliitis, an uncommon joint involvement of rheumatoid arthritis, and accelerated subcutaneous nodulosis after treatment with adalimumab. Introduction RA is a chronic, autoimmune disorder that primarily affects peripheral synovial joints [1]. The axial skeleton is usually spared other than the cervical spine, particularly C1 to C2 [1]. Though sacroiliitis is a paramount sign of SpA, it can be rarely observed in RA [2]. The commonest extra-articular manifestation of RA is subcutaneous nodules, which can be accelerated with RA treatments [3]. Herein, we describe a patient presented with bilateral sacroiliitis, along with the diagnostic and therapeutic challenges we surmounted. Case presentation A-45-years-old female presented with a one-year history of inflammatory arthritis of bilateral metacarpophalangeal, wrist, and ankle joints. She also had inflammatory-type back pain with buttock pain and plantar fasciitis. The Left-sided Faber test was positive. The laboratory investigations revealed elevated inflammatory markers, negative RF and HLA-B27. MRI-SI joints revealed bilateral active sacroiliitis. She was treated as SpA with NSAIDS at first, followed by subcutaneous adalimumab due to inadequate response. Though arthritis improved following adalimumab, multiple firm subcutaneous nodules occurred in the extensor surface of the elbow and hands after six-doses of adalimumab. Biopsy was compatible with rheumatoid nodule and anti-cyclic citrullinated peptide was positive. Based on the presence of rheumatoid nodules and positive anti-CCP antibodies, the patient was diagnosed with seropositive RA and bilateral sacroiliitis, an unusual joint involvement in RA. Discussion Sacroiliitis is the paramount clinical sign in SpA [2]. However, it can be seen in a wide range of disease conditions [4]. Misclassification between SpA and RA can occur due to overlapping clinical manifestations [4]. The Rheumatoid nodule is the most common cutaneous manifestation of RA and often seen in seropositive RA and more severe disease [3]. There have been case reports of accelerated subcutaneous nodulosis in patient with RA, treated with MTX, leflunomide, azathioprine, TNF alfa inhibitors and tocilizumab [3]. Though Inflammatory back pain, active sacroiliitis, and plantar fasciitis mislead the diagnosis, rheumatoid nodules and positive anti-CCP antibodies aid the classification of RA.
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