Interobserver agreement for diagnostic MRI criteria in suspected multiple

MRI is the paraclinical test most widely used to support the diagnosis of multiple sclerosis (MS). We evaluated interobserver agree- ment in applying diagnostic criteria to MRI obtained at first presenta- tion. Five experienced observers scored 25 sets of images consisting of unenhanced T2- and gadolinium- enhanced T1-weighted images (ap- proximately half the sets were nor- mal). We scored frontal, parietal, temporal, occipital, infratentorial and basal ganglia lesions and the to- tal number of lesions on T2-weigh- ted images; periventricular, callosal, juxtacortical and ovoid lesions and those > 5 mm in maximum diame- ter; contrast-enhancing and hypoin- tense lesions. Based on a combina- tion of imaging findings patients were classified as compatible or not compatible with MS according to composite criteria. Observer con- cordance was characterised by weighted kappa values (k) and mean average difference to the median (MADM) scores. Using the raw scores, there was poor agreement for the total number of lesions on T2-weighted images, and for occipi- tal, oval, juxtacortical and hypoin- tense lesions. Moderate agreement was found for frontal, callosal, basal ganglia and large lesions on T2 weighting. Good agreement was at- tained for parietal, temporal, infra- tentorial and periventricular lesions. After dichotomisation according to accepted cut-off values, most crite- ria performed better, especially the number of lesions on T2-weighted images (P < 0.05). Good agreement was found for the criteria of Paty and Fazekas and moderate agree- ment for those of Barkhof. While experienced observers may not agree on the total number of lesions, they show quite good agreement for commonly used cut-off points and elements in the composite criteria. This validates the use of MRI in the diagnosis of MS, and the use of di- chotomised and composite criteria.