Reversible axon damage in multiple sclerosis

Axon damage might be spontaneously reversible in multiple sclerosis, according to research published online this week in Nature Medicine.

In multiple sclerosis, an inflammatory disease of the central nervous system, immune-mediated axon damage leads to permanent neurological deficits. How axon damage is initiated is not known. A classical view of multiple sclerosis is that loss of myelin ― the sheath that insulates axons to speed up the transmission of nerve signals ― is a prerequisite for axon damage.

Martin Kerschensteiner and his colleagues used imaging techniques in live mice to identify a new form of axon damage in an experimental model of multiple sclerosis. This process, termed ‘focal axonal degeneration’ (FAD), consists of sequential stages: localized damage to mitochondria within the axons, swellings of the nerve fiber and subsequent axon fragmentation. Notably, most swollen axons in their experiments persisted unchanged for several days, and some recovered spontaneously.

The team also found axonal changes consistent with FAD in lesions from patients with multiple sclerosis, highlighting the potential relevance of this form of axonal damage to the human disease.