Smouldering lesions differ from the normal lesions associated with MS, both in terms of appearance and behaviour.
Non-smouldering lesions have the ability to shrink or even to completely heal and disappear over time. This is in stark contrast to the behaviour of smouldering lesions which are thought to represent long-term, active inflammation in MS that is continuous in nature. These lesions instead remain and actively expand for many years.
A team of researchers have recently developed an imaging technique which makes it possible to visualise smouldering lesions and distinguish them from lesions that don’t smoulder based on their appearance – something that wasn’t previously possible. Using this advanced imaging technology, a distinctive, dark rim can be observed around smouldering lesions.
This rim is a visual characteristic that differentiates these lesions from others and is caused by microglia, a type of immune cell that roams the central nervous system (CNS) to remove any cell fragments, waste, and foreign material, such as bacteria and viruses. This is also why smouldering lesions are sometimes called ‘rim lesions’. Microglial activity in the CNS is normal and healthy, but that microglia can sometimes be triggered into an overactive state and that this is when they can cause disease.