To determine the prevelance of phase rim lesions (PRLs), their association with acute new T2-lesions, and to quantify normalized T1-weighted intensity (nT1), normalized magnetization transfer ratio (nMTR) and diffusion tensor imaging radial diffusivity (DTI-RD) in T2-lesions with (PRL+) and without (PRL-) phase rims, in a relapsing multiple sclerosis (RMS) population.

Chronic active lesions are a subset of MS lesions thought to be represented by phase rim signals in susceptibility-weighted MR images.

PRL data was collected at follow-up weeks 72 and 96 in a subset of RMS patients from the AFFINITY trial [] (N=44) using standardized 3-Tesla, 3D isotropic multi-echo, gradient echo MRI.

27 of 44 (61.4%) patients had at least 1 PRL at week 72 follow-up, and 11 of 44 (25.0%) had at least 4 PRLs. Approximately 10% of PRLs identified at week 72 derived from acute new lesions formed between baseline and week 72.

Acute new T2 lesions that were PRL+ were larger at first detection (median size of 392 vs 52 mm³) and had lower nMTR on average at detection and recovery stages compared to those acute new T2 lesions that were rimless.

Chronic PRLs detected within T2 lesions pre-existing at baseline showed lower nMTR and higher RD at baseline. These lesions also showed a trend of decrease in nMTR and increase in RD from baseline to week 72 compared with chronic lesions without phase rims.

These data suggest that chronic T2 lesions with phase rims have more severe tissue injury than rimless chronic lesions. The minority of new T2 lesions that developed persistent phase rims were larger in size and also associated with more severe acute tissue damage as measured by nMTR decrease.

Support: This study is funded by Biogen