During an exacerbation, what is happening to the nerve cells to cause the body to respond?
During an MS exacerbation, some unknown event or stimulus within a circumscribed region of your nervous system precipitates an inflammatory reaction. This inflammatory cycle includes breakdown of the blood brain barrier (often but not always identified briefly by contrast enhancement after an MRI) and recruitment of inflammatory cells (lymphocytes and macrophages) to the region. This less to further inflammatory injury to myelin and neural elements. Many of the initial symptoms of a relapse are caused by temporarily malfunctioning of neural elements that recover quickly. Resolution of other symptoms require clearance of myelin debris, remyelination and repair of synaptic connections. This can take weeks or months to complete. Axons that are transacted (cut in half) are irreversibly injured and cause permanent tissue damage and sometimes permanent symptoms.
The inflammation is eventually brought under control spontaneously, damaged tissue is cleared of debris, oligodendrocyte progenitor cells (the ones that make myelin) are recruited to the site of injury and attempt to repair demyelinated axons (with some partial success), dendrites sprout from neurons to create new connections and an astroglial scar is formed.
Revere (Rip) Kinkel MD
Director of the Multiple Sclerosis Program
Professor of Clinical Neurosciences
University of California San Diego