C

Reasoning: Conversion to multiple sclerosis after a demyelinating myelopathy is strongly linked to the presence of cerebrospinal-fluid–restricted oligoclonal IgG bands; when these bands are absent the likelihood of later MS is markedly reduced, making “absence of oligoclonal bands” the feature least suggestive of progression [Helfferich 2021, PMID 33509615; Monschein 2024, PMID 39433553].