"This case series is very pertinent as we have recently had a case at our centre with a lesion that looked, and behaved as a tumour, but had other features to support demyelination. Did we do a biopsy or not? The problem is if this individual had a lymphoma and we had waited to treat the lymphoma a lot would have potentially been lost. In the 4-8 weeks it takes for a lymphoma to declare itself over demyelination a lot can happen. This is why doing a biopsy, in these cases, is sometimes necessary; i.e. to make a definitive diagnosis and to start a definitive treatment ASAP."