“…Fever is usually absent or low grade • Risk factors: IV drug use, pelvic trauma, infectious endocarditis, immunosuppression, cutaneous or genitourinary infection • Imaging: on MRI, unilateral periarticular muscle edema, thick capsulitis, and extracapsular fluid collection may be useful in differentiating infectious sacroiliitis from sacroiliitis due to axSpA Whipple disease [152][153][154][155][156][157][158][159][160][161] • Large joint migratory arthralgias, abdominal pain, weight loss, and diarrhea, with or without IBP • Risk factors: occupational exposure to soil or animals • Imaging: sacroiliitis and spondylitis indistinguishable from axSpA Familial Mediterranean fever 143,[162][163][164] • Intermittent fevers, abdominal pain, large joint arthritis, enthesitis, IBP. Childhood or adolescent onset is typical, but may occur in adulthood • Risk factors: genetics (MEFV gene mutations); Turkish, Armenian, North African, Jewish, and Arab descent • Imaging: sacroiliitis indistinguishable from axSpA Sarcoidosis 149,[165][166][167][168][169][170] • IBP • Risk factors: sacroiliitis may occur most frequently in sarcoidosis limited to the thorax (thoracic lymph nodes and lungs) • Imaging: sacroiliitis indistinguishable from axSpA Spinal calcium pyrophosphate deposition disease [171][172][173] • Periodic IBP with elevated inflammatory markers • Risk factors: widespread peripheral chondrocalcinosis • Imaging: linear calcium deposition in intervertebral disks, SIJs, and/or peripheral joints Idiopathic hypoparathyroidism [174][175][176][177][178] • Hypocalcemia presentation ± back pain experience little or no pain relief with NSAIDs. 123 Furthermore, the sites of maximal point tenderness with fibromyalgia are usually not located precisely at entheseal sites.…”