Introduction: Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) with heterogenic character. Typical age of onset is between 20 and 35 years. Clinically definite multiple sclerosis (CDMS) can occur also in patients older than 50 years. This type of MS is called Late Onset Multiple Sclerosis (LOMS). Until now, the differences in clinical course, type of first symptoms, and prognosis of LOMS have not been well established. Also the MRI characteristics of patients with LOMS have not been determined. Neither conventional nor nonconventional MRI features are known to be typical for LOMS.
Clinical rationale for the study: To investigate the MRI characteristics of LOMS patients based on conventional and non-conventional techniques.
Materials and methods: Twenty patients with LOMS were included in the study and 17 patients with typical onset of MS (TOMS) served as a comparative group. The two groups were matched in terms of disease duration and EDSS score. Conventional (T1- and T2-weighted images) and non-conventional (magnetization transfer images, proton magnetic resonance spectroscopy) MRI techniques were performed in all participants. Parameters from both techniques were compared between LOMS and TOMS groups.
Results: Patients with late onset of MS had lower Brain Parenchyma Fraction (BPF) (p < 0.001) and Grey Matter Fraction (GMF) values (p = 0.008) than the TOMS group. There was no statistical differences in White Matter Fraction (WMF) values between the groups (p = 0.572). Patients with LOMS and TOMS statistically differed in the peak height (p = 0.018), peak location (p < 0.001), and MTR mean value (p < 0.001). Patients with LOMS manifested lower concentrations of NAA+NAAG and NAA+NAAG/Cr than patients with TOMS (p = 0.009 and p < 0.001 respectively). No statistical difference was found between the groups in terms of mean mIn (p = 0.346) and mean GPC+PCh (p = 0.563). We did not find a statistical difference in T1- and T2- lesion load (p = 0.1, p = 0.3 respectively) although T1/T2 lesion ratio was higher in the LOMS group.
Conclusion and clinical implications: MRI parameters in patients with LOMS differed significantly from those obtained from the TOMS group. Our results, which indicate that in LOMS patients brain tissue damage is more advanced than in TOMS patients, may contribute to a better understanding of the heterogeneity of MS.
Keywords: Late onset multiple sclerosis; brain atrophy; magnetic resonance imaging; magnetization transfer ratio; multiple sclerosis; proton magnetic resonance spectroscopy.