Infectious sacroiliitis: a retrospective, multicentre study of 39 adults.

Background: Non-brucellar and non-tuberculous infectious sacroiliitis (ISI) is a rare disease, with misleading clinical signs that delay diagnosis. Most observations are based on isolated case reports or small case series. Our aim was to describe the clinical, bacteriological, and radiological characteristics of ISI, as well as the evolution of these arthritis cases under treatment.

Methods: This retrospective study included all ISI cases diagnosed between 1995 and 2011 in eight French rheumatology departments. ISI was diagnosed if sacroiliitis was confirmed bacteriologically or, in the absence of pathogenic agents, if clinical, biological, and radiological data was compatible with this diagnosis and evolution was favourable under antibiotic therapy.

Results: Overall, 39 cases of ISI were identified in adults, comprising 23 women and 16 men, with a mean age at diagnosis of 39.7 ± 18.1 years. The left sacroiliac joint (SI) was affected in 59% of cases, with five cases occurring during the post-partum period. Lumbogluteal pain was the most common symptom (36/39). Manipulations of the SI joint were performed in seven patients and were always painful. Mean score for pain using the visual analogue score was 7.3/10 at admission, while 16 patients were febrile at diagnosis. No risk factor was found for 30.7% of patients. A diagnosis of ISI was only suspected in five cases at admission. The mean time to diagnosis was long, being 43.3 ± 69.1 days on average. Mean C-reactive protein was 149.7 ± 115.3 mg/l, and leukocytosis (leukocytes ≥ 10 G/l) was uncommon (n = 15) (mean level of leukocytes 10.4 ± 3.5 G/l). Radiographs (n = 33) were abnormal in 20 cases, revealing lesions of SI, while an abdominopelvic computed tomography (CT) scan (n = 27) was abnormal in 21 cases, suggesting arthritis of the SI joints in 13 cases (48.1%) and a psoas abscess in eight. Bone scans (n = 14) showed hyperfixation of the SI in 13 cases. Magnetic resonance imaging (MRI) (n = 27), when focused on the SI (n = 25), directed towards the diagnosis to ISI in 25 cases. Pathogenic agents were isolated in 33 cases (84.6%) by means of articular puncture (n = 16), blood culture (n = 14), cytobacteriological examination of urine (n = 2), or puncture of the psoas (n = 1).Gram-positive cocci were the mostly isolated common bacteria, with a predominance of staphylococci (n = 21). The most frequently isolated gram-negative bacillus was Pseudomonas aeruginosa (n = 3). Evolution was favourable in 37 out of 39 patients under prolonged antibiotic therapy (mean duration 3.01 ± 1.21 months).

Conclusion: Our series confirmed that the clinical manifestations of ISI usually lead to delayed diagnosis. Based on our results, we suggest performing an MRI of the spine and SI in clinical situations characterised by lumbogluteal pain and symptoms of an infectious disease, such as fever.