Lesions will still show up without contrast; what won't show up without contrast would be "enhancing" lesions typical of ms plaque that is currently active.
My inital scans were done without contrast because the neurologist was looking for a tumour and something to explain the facial neuralgia I was experiencing. I ended up needing a second set of mris with contrast as per ms protocol instead.
So it depends what your doctor is looking for with this initial scan. If you are worried that no contrast has been ordered, please know that if there is anything indicative of ms lesion-wise, they will do further scans.
Did your MRI without contrast show any lesions or only when they did the contrast?