Interobserver agreement for diagnostic MRI criteria in suspected multiple sclerosis

MRI is the paraclinical test most widely used to support the diagnosis of m ultiple sclerosis (MS). We evaluated interobserver agreement in applying di agnostic criteria to MRI obtained at first presentation. Five experienced o bservers scored 25 sets of images consisting of unenhanced T2- and gadolini um enhanced T1-weighted images (approximately half the sets were normal). W e scored frontal, parietal, temporal, occipital, infratentorial and basal g anglia lesions and the total number of lesions on T2-weighted images; periv entricular, callosal, juxtacortical and ovoid lesions and those > 5 mm in m aximum diameter; contrast-enhancing and hypointense lesions. Based on a com bination of imaging findings patients were classified as compatible or not compatible with MS according to composite criteria. Observer concordance wa s characterised by weighted kappa values (kappa) and mean average differenc e to the median (MADM) scores. Using the raw scores, there was poor agreeme nt for the total number of lesions on T2-weighted images, and for occipital , oval, juxtacortical and hypointense lesions. Moderate agreement was found for frontal, callosal, basal ganglia and large lesions on T2 weighting. Go od agreement was attained for parietal, temporal, infratentorial and perive ntricular lesions. After dichotomisation according to accepted cut-off valu es, most criteria performed better, especially the number of lesions on T2- weighted images (P < 0.05). Good agreement was found for the criteria of Pa ty and Fazekas and moderate agreement for those of Barkhof. While experienc ed 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 composi te criteria. This validates: the use of MRI in the diagnosis of MS, and the use of dichotomised and composite criteria.