The differential diagnosis of multiple sclerosis can present specific challenges in patients from Latin America, Africa, the Middle East, eastern Europe, southeast Asia, and the Western Pacific. In these areas, environmental factors, genetic background, and access to medical care can differ substantially from those in North America and western Europe, where multiple sclerosis is most common. Furthermore, multiple sclerosis diagnostic criteria have been developed primarily using data from North America and western Europe. Although some diagnoses mistaken for multiple sclerosis are common regardless of location, a comprehensive approach to the differential diagnosis of multiple sclerosis in Latin America, Africa, the Middle East, eastern Europe, southeast Asia, and the Western Pacific regions requires special consideration of diseases that are prevalent in those locations. A collaborative effort has therefore assessed global differences in multiple sclerosis differential diagnoses and proposed recommendations for evaluating patients with suspected multiple sclerosis in regions beyond North America and western Europe.
There is no consensus regarding the classification of optic neuritis, and precise diagnostic criteria are not available. This reality means that the diagnosis of disorders that have optic neuritis as the first manifestation can be challenging. Accurate diagnosis of optic neuritis at presentation can facilitate the timely treatment of individuals with multiple sclerosis, neuromyelitis optica spectrum disorder, or myelin oligodendrocyte glycoprotein antibody-associated disease. Epidemiological data show that, cumulatively, optic neuritis is most frequently caused by many conditions other than multiple sclerosis. Worldwide, the cause and management of optic neuritis varies with geographical location, treatment availability, and ethnic background. We have developed diagnostic criteria for optic neuritis and a classification of optic neuritis subgroups. Our diagnostic criteria are based on clinical features that permit a diagnosis of possible optic neuritis; further paraclinical tests, utilising brain, orbital, and retinal imaging, together with antibody and other protein biomarker data, can lead to a diagnosis of definite optic neuritis. Paraclinical tests can also be applied retrospectively on stored samples and historical brain or retinal scans, which will be useful for future validation studies. Our criteria have the potential to reduce the risk of misdiagnosis, provide information on optic neuritis disease course that can guide future treatment trial design, and enable physicians to judge the likelihood of a need for long-term pharmacological management, which might differ according to optic neuritis subgroups.