The effect of ocrelizumab on Balo's tumefactive lesion: A case report

Balo's concentric sclerosis (BCS) is a rare subtype of multiple sclerosis. Advanced MRI metrics, such as magnetization transfer ratio (MTR), fractional anisotropy (FA), mean diffusivity (MD), and the ratio of total N-acetylaspartate concentration/total creatine concentration (tNAA/tCr) using proton magnetic resonance spectroscopy (¹H-MRS), are commonly used in research studies to investigate the effect of a disease modifying therapy (DMT). We report a patient diagnosed with BCS, receiving ocrelizumab, and provide a comparison of the lesion volume, T1-gadolinium lesion volume, MTR, FA, MD, and MRS metrics at baseline, 6- and 12-month follow-up. There was a reduction in Balo's lesion volume on fluid-attenuated inversion recovery (FLAIR) imaging observed in our patient from baseline (23.925 mL) to 12-month follow-up (2.391 mL), with the largest decrease from baseline to 6-month follow-up (3.650 mL). There was no T1-gadolinium enhancement seen at month 6 and 12. The MTR of the lesion did not change significantly (baseline = 50.9%, 6-month = 49.9%, 12-month =50.1%) but the FA increased from 0.188 (at baseline) to 0.304 (at 6 months), while the 12-month follow-up FA was 0.297. We also noted a reduction in MD from baseline (1.333 × 10^-3 mm²/s) to 6-month follow-up (1.037 × 10^-3 mm²/s), while the 12-month follow-up MD was 1.086 × 10^-3 mm²/s. There was a 10.3% increase in tNAA/tCr from 1.583 (at month 0) to 1.747 (at month 12). Our results demonstrate for the first time a direct effect of ocrelizumab on BCS lesions. To validate our findings, more observations are needed in a larger group of BCS patients.