We tend to focus on the most readily seen. This is a clear strength, but also may at times be a limitation. Regarding multiple sclerosis (MS), the unpredictable and often dramatic appearance of clinical relapses and focal magnetic resonance imaging (MRI) abnormalities tend to catch our attention. However, these events can often obscure more insidious, but no less important, destructive changes, such as irreversible disability progression and MRI-evident brain atrophy. Perhaps it is a matter of time scale. Clinical observation detects focal events (relapses) relatively often, typically on an at least yearly basis; focal MRI events occur much more frequently, even monthly, if looked for. In contrast, due in part to the week-to-week variability of MS and the protracted nature of its progression, permanent and irreversible worsening of MS-related disability often takes longer to become unequivocally recognized by patient and physician. Progressive brain atrophy, also slowly developing, can be even more challenging to detect and accurately monitor, and requires sensitive and reproducible measurement tools applied to serially obtained MRI scans.
Phillips JT. What Causes Multiple Sclerosis to Worsen?. Arch Neurol. 2007;64(2):167-168. doi:10.1001/archneur.64.2.167