LAUSR

Background The sacroiliac joint is a rare localization of septic arthritis whose diagnosis is often delayed due to a heterogeneous and non-specific clinical presentation. The gold standard for diagnosis in osteo-articular infections is MRI, but its emergency access is sometimes difficult and the acquisition time of this imaging mode is long. Objectives To look for early CT scan signs suggestive of infectious sacro iliitis. Methods In a monocentric retrospective study at the BesanÇon University Hospital between January 2013 and March 2018, we analyzed the cases of septic arthritis of the sacroiliac joints in subjects over 18 years of age. We studied the clinical, biological and imaging data of each patient. Results 7 cases of infectious sacro-iliitis were collected. The characteristics of the patients were: 57% male, average age 44.1 years, left sacroiliac in 4 cases, fever in 57%, average CRP 184mg/l, average leucocytes 12500/ml. 3 patients were immunocompromised, 1 patient was postpartum. In 5 cases, bacteriological documentation was found (1 multisensitive aureus staphylococcus, 2 streptococci, 2 Gram negative bacilli). In the last 2 cases, no germ could be detected due to antibiotic therapy initiated before their hospitalization, but the clinical presentation, biology, imaging and evolution under antibiotics were in favour of an infectious etiology. The 7 patients underwent a pelvic CT scan during their hospitalization, on average 6 days after the beginning of their symptoms. 4 early signs in favour of the diagnosis of infectious sacro iliitis could be identified: fat infiltration in front of the sacroiliac joint in 86% of cases, bulging and elevation of the anterior part of the joint capsule in 43%, swelling of the piriform (71%) and iliac (71%) muscles on the sacroiliac side. All patients had at least 1 positive sign out of 4, 86% had at least 2. In 1 case, signs of osteitis were present. In 4 out of 7 cases, the injection of iodized contrast medium did not provide any additional element compared to the non-injected sequences. 5 patients underwent an MRI after the scan, which confirmed the signs in favour of the infectious nature of sacroilitis. MRI detected in one case an aspect of osteomyelitis of the sacrum and iliac bone, but also a hypersignal of the joint space on the T2 sequences (80%) and a better visualization of abscesses. In the literature, there is data on the interest of the CT scan for the diagnosis of infectious sacro iliitis (1) but there is no precise description of the early signs suggestive apart from the signs of osteitis, which appear later. Hermet et al (2) advised to be careful if the scan is performed within 3 days after the onset of symptoms, but our short series shows that some signs are positive even if the pelvic scan is performed very early. The interest of the scanner, in addition to its rapid access and acquisition, allows on the injected sequences to rule out differential infectious diagnoses of abdominal-pelvic or gynaecological origin, the clinic being sometimes put in defect. Conclusion Despite its radiant nature, the scanner can be a preferred accessible alternative to MRI for the diagnosis of infectious sacro iliitis with the detection of 4 signs of early onset. References [1] Matt M,et al. Med Mal Infect 2018; pii: S0399-077X(16)30754-5. [2] Hermet M, et al. BMC Infect Dis 2012;12:305. Disclosure of Interests None declared