Which is the only drug effective in improving EDSS in multiple sclerosis?

The statement only drug effective in improving EDSS seems to be wrong because many drugs have shown to reduce disease severity on EDSS scores. Expanded disability status score(EDSS) is a scoring system for MS where high score means worsening neurological dysfunction. Maximum reduction in EDSS is seen in natalizumab group. Ref :Harrisons 18th ed.