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In patients with primary progressive (PP) multiple sclerosis, brain MRI lesion activity and burden are low, despite the presence of severe neurological impairment. On the contrary, the degree of cord atrophy and diffuse tissue damage in the brain and cervical cord have been found to be associated with clinical disability. Against this background, this study aimed at providing an in vivo indirect assessment of brain and cervical cord pathology in a large cohort of PP multiple sclerosis patients, using conventional MRI and magnetization transfer imaging (MTI). Ninety-one PP multiple sclerosis patients, 36 secondary progressive (SP) multiple sclerosis patients and 30 healthy controls underwent brain and cervical cord MRI scans, using dual echo (brain) or fast short-tau inversion recovery (cervical cord) MTI and T(1)-weighted sequences. For the brain, T(2) hyperintense and T(1) hypointense lesion volumes were calculated and the volume of the whole of the brain tissue measured. For the cervical cord, the number and burden of lesions and the cross-sectional area were assessed. MTI scans were post-processed and analysed to obtain magnetization transfer ratio (MTR) histograms from the whole of the brain and cervical cord tissue and from the normal-appearing brain tissue in isolation. In PP multiple sclerosis patients, brain, normal-appearing brain tissue and cervical cord MTR histogram-derived metrics revealed the presence of diffuse tissue damage whose characteristics did not significantly differ from those of SP multiple sclerosis patients, even though SP multiple sclerosis patients had higher MRI-visible lesion burdens. None of the correlations between MRI or MTI measures obtained from the brain and the cord were significant. PP multiple sclerosis patients' disability was significantly, albeit weakly associated with a composite MR model including measures of loss and intrinsic damage of cervical cord tissue. Our data indicate the presence of a diffuse tissue damage undetectable by conventional MRI in PP multiple sclerosis patients, whose extent seems to match that of SP multiple sclerosis patients with similar levels of disability. They also suggest that the severity of multiple sclerosis pathology in the cervical cord is one of the factors contributing to neurological impairment in PP multiple sclerosis.

ObjectiveTo assess (a) the correlations between magnetisation transfer ratio (MTR) histogram derived measures of the brain and the cervical cord from patients with different multiple sclerosis phenotypes and (b) the correlation between these metrics and clinical disability. Magnetisation transfer imaging is sensitive to the most destructive aspects of multiple sclerosis pathology. Magnetisation transfer ratio histogram analysis encompasses the macroscopic and the microscopic lesion burdens.MethodsSeventy seven patients with multiple sclerosis were studied (40 relapsing-remitting (RR), 28 secondary progressive (SP), and nine primary progressive (PP)). For the brain, we obtained dual echo, T1 weighted, and gradient echo (GE) scans (with and without an MT saturation pulse). For the cervical cord, fast short tau inversion recovery (STIR) and GE scans (with and without an MT saturation pulse) were obtained. Brain T2 and T1 weighted lesion volumes (LVs) were measured. The number and length of cord lesions on fast STIR scans were assessed. Magnetisation transfer ratio maps were created from GE images and MTR histograms of the entire brain and cervical cord were obtained.ResultsBrain T1 LV, and number and size of cord lesions were significantly higher and brain MTR histogram peak location was significantly lower in patients with SPMS than those with RRMS or PPMS. Cord MTR histogram peak location was also significantly lower in patients with SPMS than in those with RRMS. The univariate correlations between MTR histogram derived metrics obtained from the brain and the cervical cord were all non-significant, with the exception of that between average brain MTR and cord MTR histogram peak location. On a multivariable analysis, both increasing brain T2 LV and decreasing cord MTR histogram peak location values were significantly associated with a higher probability for patients to have SPMS or to have locomotor disability.ConclusionsThis study shows that the extent and severity of tissue damage in the brain and cervical cord are both relevant to determine disability in multiple sclerosis and that the assessment of brain and cord pathology provides complementary information.