DIT 2005 The appearance of a new T2 lesion on a scan compared to a reference or baseline scan performed at least 30 days after the onset of the initial clinical event.

In clinical practice, however, there is reason not to postpone a first MRI until after 30 days of clinical onset, which would result in an extra MRI scan to confirm a diagnosis.

DIT 2010 allows a new T2 lesion to establish DIT irrespective of the timing of the baseline MRI.