PENTAGON is an observational, non-interventional, multicenter, prospective cohort study conducted at approximately 20 neurology centers and affiliated radiology centers across Germany. It investigates whether loss of thalamic volume (TVL) is an independent driver of disability progression in patients with relapsing-remitting multiple sclerosis (MS). The study observes two groups: patients with active MS (receiving or about to receive first- or second-line disease-modifying therapies) and patients with progressive MS. Over a 24-month primary observation period - extendable to 72 months - MS-related disability is measured with the Expanded Disability Status Scale (EDSS), and whole-brain and thalamic volumes are quantified from standardized high-resolution T1-weighted MRI using validated deep-learning methods. The primary objective is to demonstrate that the change in MS-related disability over 24 months is inversely associated with the change in thalamic volume over the same period. No procedures beyond routine clinical care are required.