Background Prevalence of structural lesions on MRI in recent onset axial spondyloarthritis (axSpA) patients (pts) and back pain pts is unknown
Objectives To investigate the prevalence of structural lesions on MRI in these pts
Methods Pts with back pain (≥3 months, ≤2 years, onset <45 years) from the 5 centers were included in the SPondyloArthritis Caught Early (SPACE)-cohort. Pts underwent MRI of the sacroiliac joints (MRI-SI). MRIs-SI were scored by 3 well-calibrated readers independently for ankylosis, sclerosis, erosions, and fatty lesions (FL) (MRI T1-weighted images; STIR images viewed simultaneously). Erosions, sclerosis and FL were defined according to the MORPHO definition1 (≥1 lesion on ≥2 consecutive slices or ≥2 lesion on 1 slice); ankylosis as 1 lesion on ≥1 slice. Lesions were considered present if 2/3 readers agreed. Prevalence based on several cut-offs of structural lesions were calculated. Pts were grouped according to the ASAS axSpA criteria2 [imaging-arm (mNY+, mNY-), clinical arm], no-SpA and possible SpA
Results Pts with MRI-SI data were included (n=299). If defined as ≥1, all structural lesions except ankylosis were frequent in all groups; in decreasing frequency in mNY+, MRI+mNY-, clinical-arm, possible SpA and no-SpA. The higher the cut-offs, the better discrimination between the imaging-arm and no/possible SpA; the clinical-arm close to no/possible SpA. To define a proper cut-off for the presence of structural lesions in axSpA, the false-positive percentage in no-SpA pts should be low. We defined possible cut-offs based on the acceptance of ≤10% (italics) and ≤5% (bold) false-positives (table). E.g. if ≥4 structural lesions are present, false-positives are 6.0% and 5.2% resp., with a frequency of 61.5% and 43.5% in the mNY+ and MRI+mNY- subgroups.
Conclusions Prevalence of erosions, sclerosis and FL on MRI-SI is high in axSpA pts but also in no-SpA pts. Higher cut-offs than ≥1 lesion are needed to reduce false-positives; also with higher cut-offs structural lesions are frequent in early axSpA pts. These data suggest that with appropriate cut-offs, structural lesions might be helpful in defining sacroiliitis on MRI
Weber A&R 2010;62:3048-58
Rudwaleit ARD 2009;68:777-83
Disclosure of Interest None Declared
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