Background/Purpose: To study other disease conditions which can present with bone marrow edema of the sacroiliac joints mimicking spondyloarthritis(SpA).

Methods: In a retrospective study of 581 patients from January 2007 to January 2014 for inflammatory back pain datas, including clinical manifestations, laboratory examinations, imaging manifestations and sacroiliac joint biopsy pathological features of these patients were reviewed. All of these patients from Chinese PLA General Hospital. The Images were read independently by at least 2 experienced rheumatologists.

Results: Of the 581 patients, 455 (78.3%) were male, and 436 (75%) cases were diagnosed Ankylosing Spondylititis(AS)/SpA. HLA-B27 positivity rate was 87% among those diagnosed with AS/SpA, Among the 145 patients whose diagnosis was not AS/SpA, HLA-B27 positivity rate was only 8% in 145 patients. 46, 40 and 30 patients had an infectious etiology (pyogenic sacroiliitis/tuberculous infectious sacroiliitis/Brucellar infectious sacroiliitis), sclerosing osteitis or hypophosphatemia osteomalacia (HO) respectively. Other less common diagnoses included diffuse idiopathic bone hypertrophy, palmoplantar pustulosis arthritis and sacroiliac joint gout. The causes of HO included 15 cases of tumor-induced osteomalacia, 4 cases of long-term oral adefovir dipivoxil, 3 cases of Fanconi syndrome, 2 cases of hyperparathyroidism, 2 cases of Sjogren’s syndrome complicated with renal tubular acidosis. Patients with infectious sacroiliitis presented with MRI abnormalities which included bone marrow edema, erosion of bone and joint, 44 of the 46 patients who had an infectious sacroiliitis show adjacent muscle involvement in MRI.

Conclusion: Sacroiliitis not due to AS is quite common in daily practice.  Rheumatologists should suspect a different diagnosis when patients respond poorly to NSAIDs, have unexplained low grade fever or other clinical manifestations which cannot be fully explained by AS/SpA. This is even more important when making the decision of using anti-TNF therapy or other immunosuppressive agents.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/sacroiliitis-misdiagnosed-as-spondyloarthritis-clinical-analysis-of-581-cases/