This clinical trial is focused on studying a condition known as Primary Progressive Multiple Sclerosis (PPMS). This is a type of multiple sclerosis where the disease gradually worsens over time without any periods of improvement. The study is evaluating a treatment called Ocrelizumab, which is given as a solution through an intravenous infusion, meaning it is administered directly into the bloodstream through a vein.

The purpose of the study is to assess how effective and safe Ocrelizumab is for adults with PPMS. Participants in the study will receive either Ocrelizumab or a placebo, which is a substance with no active medication. The study will monitor the time it takes for participants to experience a progression in their symptoms, such as worsening hand function or an increase in disability, as measured by specific tests. These tests include the 9-Hole Peg Test (9-HPT), which measures hand dexterity, and the Expanded Disability Status Scale (EDSS), which assesses disability in people with multiple sclerosis.

Throughout the study, participants will undergo regular MRI scans to check for changes in the brain and spinal cord. The study will also track any side effects or adverse events that occur. The trial is designed to last for several years, allowing researchers to gather comprehensive data on the long-term effects of Ocrelizumab in treating PPMS.