A 35 year old woman presents with a band-like sensation around her abdomen, leg weakness and bladder dysfunction. On questioning she reveals that she had an episode around a year ago, where she experienced left eye pain and problems with her vision, this resolved within a few weeks and she did not seek medical attention. On examination she has increased tone in her legs, bilateral weakness and hyperreflexia. What is/are the key factor(s) required to make a diagnosis of multiple sclerosis?