The diagnosis of multiple sclerosis: pinpointing the concept of "no better explanation"

Background: Since the first appearance of McDonald’s diagnostic criteria for Multiple Sclerosis (MS), it was clear that beyond the demonstration of the disease dissemination in space and time, a crucial role in the diagnostic work up would have been played by the exclusion of other neurological diseases. Aim of this study is to provide an accurate picture of the main diseases that can mimic MS in the “real world” setting of a large number of specialist MS centres. Methods: Prospective, observational clinical and radiological study Including all patients presenting with symptoms suggestive of MS, in which a further examination was required in order to exclude or confirm MS diagnosis. Each patient after a regular diagnostic workup (including magnetic resonance imaging, visual evoked potentials, blood and cerebrospinal fluid examinations) was included in a 2 years clinical and radiological follow up. Results: In the first 2 months of recruitment, 300 patients were included and underwent clinical, imaging and paraclinical (blood and CSF) examinations. Among these patients, in 123 (41.3%) it has been possible to diagnose MS according to the most recently revised MS diagnostic criteria, in 55 (18.3%) a different diagnosis was made and in the remaining 121 (40.3%) patients a clinical and radiological follow up was required to clarify the diagnosis. Among the 55 patients in which a MS diagnosis was excluded and other diagnoses were already possible, the most frequent diagnoses were migraine (in 15 cases), vascular encephalopathy including PTO (in 13 cases), recurrent optic neuritis (in 2 cases), systemic erythematous lupus (in 2 cases), dizziness (in 2 cases), neuroBechet’s disease (in 2 cases), neuromyelitis optica (in 2 cases). Discussion: Our preliminary analysis confirm that according to the new diagnostic criteria, the MS diagnosis can be made at the end of diagnostic work-up after the first clinical evaluation in almost 40% of the patients presenting with symptoms suggestive of MS. Migraine and vascular encephalopathy are by far the most frequent alternative diagnosis, while, so far, no infective diseases have been observed. Results of our study will be helpful to recommend an appropriate diagnostic algorithm based on the most frequent conditions entering the differential diagnosis with MS.