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.