Misdiagnosis of sacroiliac joint gout as ankylosing spondylitis: Solving the diagnostic dilemma with dual-energy computed tomography.

Gout rarely affects the axial joints, and sacroiliac joint involvement is exceptionally uncommon. This report describes the case of a 30-year-old female with a family history of gout who had recurrent knee swelling and low back pain for 2 years, initially misdiagnosed with ankylosing spondylitis. Laboratory findings showed episodic hyperuricemia and elevated inflammatory markers, while MRI revealed bilateral sacroiliitis and bone island in the right sacroiliac joint. HLA-B27 was negative, and no family history of psoriasis or ankylosing spondylitis was noted. The atypical presentation of inflammatory low back pain, along with episodic joint redness, swelling, and pain, prompted further investigation. Dual-energy computed tomography confirmed urate crystal deposition in the sacroiliac joint and knees, accompanied by bone erosion, leading to a final diagnosis of primary sacroiliac joint gout. The patient's symptoms improved significantly after being treated with diclofenac and benzbromarone. This case emphasizes dual-energy computed tomography's diagnostic utility in differentiating gouty arthritis from inflammatory sacroiliitis, especially in patients with atypical presentations, family history of gout, or hyperuricemia. Although rare, axial joint gout should be considered a differential diagnosis for axial and large joint pain. Dual-energy computed tomography provides critical insights, allowing the accurate localization of urate deposits and preventing misdiagnosis or delayed treatment. This case highlights the need for increased clinical awareness and appropriate imaging for rare presentations of gout.