Grey:white matter ratio at diagnosis and the risk of 10‐year multiple sclerosis progression

Background and purpose Grey matter ( GM ) and white matter ( WM ) are both affected in multiple sclerosis ( MS ). WM is predominantly involved in inflammatory demyelination of relapsing–remitting MS ( RRMS ), whereas GM is predominantly involved in neurodegenerative processes of secondary progressive MS . Thus, we investigated the ratio between GM and WM volumes in predicting MS evolution. Methods The present 10‐year retrospective cohort study included 149 patients with newly‐diagnosed RRMS , undergoing magnetic resonance imaging for segmentation and brain volumetry. The ratio between GM and normal‐appearing WM ( NAWM ) volumes was calculated for each subject. Outcome measures of interest were Expanded Disability Status Scale ( EDSS ) progression, reaching EDSS 4.0 and conversion to secondary progressive (SP) MS. Results During a period of 10.6 ± 2.4 years, a median 1.5 EDSS progression was observed (range 0–5.5), 54 subjects (36.2%) reached EDSS 4.0 and 30 subjects (20.1%) converted to SP . With ordinal logistic regression models, EDSS progression was associated with GM : NAWM ratio (coefficient, −2.918; 95% CI , −4.739–1.097). With Cox regression models, subjects with higher GM : NAWM ratio at diagnosis had a 90% lower rate of reaching EDSS 4.0 (hazard ratio, 0.111; 95% CI , 0.020–0.609) and of converting to secondary progressive MS (hazard ratio, 0.017; 95% CI , 0.001–0.203) compared with subjects with lower GM : NAWM ratio. Conclusions The GM : NAWM ratio is a predictor of disability progression and of SP conversion in subjects with newly diagnosed RRMS , suggesting that GM and NAWM are variably affected in relation to disease evolution from the early phases of MS .