Uncovering alternative diagnoses in patients with clinical syndromes suggestive of multiple sclerosis: A transversal study from the prospective Barcelona CIS cohort

BACKGROUND: It is essential to exclude alternative diagnoses to diagnose multiple sclerosis (MS). However, detailed descriptions of alternative diagnoses in patients with suspected MS presenting with clinically isolated syndrome (CIS) are limited. OBJECTIVES: To describe alternative diagnoses in patients presenting with CIS suggestive of MS. METHODS: We conducted a descriptive analysis of patients from the Barcelona CIS cohort including subjects under 50 years of age with a CIS suggestive of MS but later diagnosed with conditions other than MS. We collected clinical, biological, and radiological data, and described the alternative etiologies identified.RESULTS: Among 1468 patients in the Barcelona CIS cohort, 100 (6.8%) were diagnosed with an alternative condition. The most common neurological syndrome was optic neuritis (43.0%). Four patients (4.0%) had inflammatory-demyelinating lesions in at least two typical MS topographies on baseline magnetic resonance imaging (MRI), and 2 (2.0%) met the 2017 McDonald MS criteria. The most common etiologies were immune-mediated diseases (42.0%), especially MOGAD, followed by functional neurological disorders (15.0%) and vascular disease (10.0%). CONCLUSION: The range of alternative diagnoses encountered during the MS diagnostic process highlights the need to rule out better explanations than MS. However, current MS diagnostic criteria effectively identify patients without MS in this context.