Severe tertiary hyperparathyroidism as a rare mimicker of sacroiliitis.

A 42-year-old female patient was referred for rheumatology evaluation due to suspected sacroiliitis, incidentally detected on a pelvic computerized tomography (CT). Her medical history was notable for chronic kidney disease (CKD) complicated with tertiary hyperparathyroidism. A few months before rheumatologic evaluation, she underwent total parathyroidectomy. CT imaging was reviewed revealing prominent erosions of the iliac articular surfaces of the sacroiliac joints. Given the absence of inflammatory low back pain and the patients history of severe hyperparathyroidism, the sacroiliac changes were interpreted as most likely secondary to metabolic bone disease rather than inflammatory spondyloarthropathy. CT findings in hyperparathyroidism may include widening of joint spaces and irregularity of the articular surfaces. Involvement of the sacroiliac joints often manifests as erosions on the iliac sides, occasionally accompanied by reactive sclerosis. These features can mimic those seen in spondylarthritis, making the differential diagnosis challenging.