MAGNETIC-RESONANCE-IMAGING (MRI) FOR DETECTION OF ACTIVE SACROILIITIS- A PROSPECTIVE-STUDY COMPARING CONVENTIONAL RADIOGRAPHY, SCINTIGRAPHY, AND CONTRAST-ENHANCED MRI

Objective. Sacroiliitis is often difficult to diagnose in the absence of radiographic alterations. For the diagnosis of active sacroiliitis, plain radiography, scintigraphy, and contrast enhanced magnetic reson ance imaging (MRI) were evaluated in a prospective study. Methods, In 44 consecutive patients with complete clinical and laboratory evaluati on, plain radiographs, quantitative sacroiliac (SI) scintigraphy, and MRI were performed to evaluate the contribution of these imaging techn iques to the diagnosis of active sacroiliitis. Scintiscanning and MRI were done in 20 control subjects to define the normal range of imaging findings. We determined the sensitivity and specificity for each imag ing method using a reference standard based on clinical symptoms of in flammatory low back pain with or without laboratory signs, and on clin ical and radiographic followup during 1.5-2.5 years to confirm diagnos is. Results, MRI was most sensitive (95%) and superior to quantitative SI scintigraphy (48%) or conventional radiography (19%) for the detec tion and confirmation of active sacroiliitis. For the assessment of in flammatory signs, MRI had higher specificity (100%) than scintigraphy (97%) or plain radiography (47%). At repeat MRT after 2-30 months, the re was persistent pathologic signal intensity in the subchondral bone area despite clinically successful antiinflammatory drug therapy. Conc lusion. For the assessment of active changes in the synovial portion a nd the subchondral bone marrow, contrast enhanced MRT is superior to q uantitative SI scintigraphy or conventional radiography. MRI picks up an additional 75% of early cases not diagnosed by plain radiography. S cintigraphy is only of limited value. Persistent pathologic signal int ensity in the subchondral bone marrow seems to be closely associated w ith previous inflammatory episodes, thus limiting specificity of MRT f or active sacroiliitis. Based on our findings we suggest an algorithm for the evaluation of patients with suspected active sacroiliitis.