CHI3L1 and primary progressive multiple sclerosis: Biomarker comparisons between clinical phenotypes have yielded interesting clues where radiological (73) (extent of Gd lesions or focal WM lesion load), histological (74) (extent of meningeal infiltrates or extent of white matter lesion) and inflammation-associated markers (75, 76) [CD5L or chitinase-3-like protein 1 (CHI3L1)], as well as select metabolites (77) (ascorbate), were found to differ between SPMS and PPMS.