Beyond the 2024 McDonald criteria for defining and diagnosing multiple sclerosis.

The multiple sclerosis community has made continuous improvements to historical diagnostic criteria by incorporating newer technology and recognising the need to diagnose MS at an early stage, when disease-modifying therapy may be more effective. Despite these improvements, we do not know how well these criteria perform in clinical practice. Therefore, a new approach may be needed going forward to incorporate lessons learned from other complex diseases to define the sensitivity and specificity of the criteria and to improve them. This is important to avoid misdiagnosis and overdiagnosis and, as a consequence, inappropriate treatment. We therefore propose a tiered process for developing and validating diagnostic criteria in the future. As part of this process, we suggest diagnostic criteria underpinned by a biological definition of MS, informed by deductive reasoning, and applying lessons learnt from other disease areas. In conclusion, we recommend that the MS community initiate a prospective international study to validate and compare MS diagnostic criteria. The ultimate aim is to facilitate the identification of individuals with early biological disease and to enhance overall diagnostic accuracy. It is important to develop a diagnostic framework for MS prevention that does not necessarily rely on clinical or radiological confirmation of MS, i.e., time to a first clinical or radiological event.