Objective:To investigate the use of a quantitative diffusion-weighted imaging (DWI) tool for measuring inflammation of the sacroiliac joints (SIJs) in enthesitis-related arthritis (ERA).Methods:A retrospective study was performed with institutional review board approval. Subjects were adolescents who had undergone MRI of the SIJs since January 2010. 10 patients with a clinical diagnosis of ERA and 10 controls with a clinical diagnosis of mechanical back pain were assessed. Axial T1 weighted, short tau inversion recovery (STIR) and DWI (b-values 0, 50, 100, 300 and 600 mm2 s−1) images were acquired. Apparent diffusion coefficient (ADC) maps were generated using a monoexponential fit. On each of four slices, two to three linear regions-of-interest were placed on each joint. Normalized ADC (nADC) values were defined as joint ADC divided by a reference ADC derived from normal sacral bone. STIR images were scored using a modification of an established technique. The correlation between nADC values and STIR scores was evaluated using Spearman's rank correlation.Results:Mean nADC values were significantly higher in cases than in controls (p = 0.0015). There was a strong correlation between STIR scores and nADC values (R = 0.85).Conclusion:ADC values are significantly increased in inflamed SIJs compared with controls. There is a good correlation between this diffusion-based method and STIR scores of inflammation.Advances in knowledge:We have described and provisionally validated a method for quantifying the severity of inflammation in the SIJs in ERA using ADC measurements. This method is quick, is reproducible and could potentially be automated.

ObjectiveTo describe and profile abnormalities of the lumbar spine in a cohort of patients with enthesitis-related arthritis (ERA) as compared to a control group of adolescents with mechanical back pain.MethodsWe performed a retrospective review of magnetic resonance imaging (MRI) lumbar spine scans of 79 patients (58 cases, 21 controls). The study was covered by institutional review board approval and informed consent was obtained for review of all clinical investigations. Images were reviewed by an expert MRI reader who was blinded to clinical details. The presence or absence of morphologic features of enthesitis, apophyseal joint synovitis, and inflammation of posterior elements was assessed at each lumbar vertebral level. The apophyseal joint inflammation was graded from 0 to 3 using a grading system that was adapted from one used in adults with inflammatory facet osteoarthropathy. STATA software was used for data analysis.ResultsOne or more abnormalities of the lumbar spine were found in 39 (67%) of 58 cases and sacroiliitis was present in 45 (78%) of the cases. Apophyseal joint synovitis was seen in 22 (38%) cases and in 1 (5%) control patient. This difference was highly significant (P = 0.004). Inflammatory changes in the interspinous ligaments were seen in a higher percentage of cases than controls and this observation was of statistical significance (P = 0.04).ConclusionStatistically significant inflammation of the lumbar apophyseal joints and interspinous ligaments was seen in our cohort of ERA patients, most of whom have concurrent sacroiliitis. This could be contributing to back pain in these patients.

DWI measurements reflect the response to TNF inhibitor treatment in ERA patients with sacroiliitis as defined using radiological criteria and may also reflect clinical response. DWI is more objective than visual scoring and has the potential to be automated. ADC/nADC could be used as biomarkers of sacroiliitis in the clinic and in clinical trials.

PurposeTo determine the extent to which apparent diffusion coefficient (ADC) values vary with skeletal maturity in adolescent joints.Materials and MethodsA retrospective study was performed with Institutional Review Board (IRB) approval. We used a picture archiving and communication system (PACS) search to identify and recruit all adolescents who had undergone 1.5T magnetic resonance imaging (MRI) of the sacroiliac joints (SIJs) between January 2010 and June 2015, and had no evidence of sacroiliitis and normal inflammatory markers. In all, 55 individuals were assessed. For each patient, coronal and sagittal images of the sacrum were visually analyzed to determine sacral maturity. Patients were divided into three groups depending on the degree of fusion of the sacral segmental apophyses: “Fused,” “Partial,” and “Unfused.” For each group, SIJ ADC was measured using a linear region‐of‐interest technique.ResultsMean ADC values were 690 × 10−6 mm2/s in the fused group, 720 × 10−6 mm2/s in the partial group, and 842 × 10−6 mm2/s in the unfused group. ADC values were significantly higher in the unfused group than in the fused group (P = 0.046). ADC values were also higher in unfused subjects than partially fused subjects (P = 0.074).ConclusionJoint ADC values are higher in skeletally immature (unfused) patients than in skeletally more mature (fused) patients. ADC values measured in the unfused group overlap with those previously reported in sacroiliitis. These results suggest that ADC measurements in adolescent joints must be interpreted in light of joint maturity. Joint immaturity may lead to misdiagnosis of sacroiliitis, since immature juxta‐articular bone may appear similar to inflammation. J. Magn. Reson. Imaging 2016. J. Magn. Reson. Imaging 2016;44:556–564.