GFAP and myeloid sarcoma: In MS, the disruption of astrocytic end-feet around blood vessels and the appearance of hypertrophic astrocytes at the rim of WM lesions is one of the earliest histopathological features in the acute MS lesion, and astrogliosis, defined as increased expression of glial fibrillary acidic protein (GFAP), occurs alongside chronic demyelination and axon loss in the core of demyelinated lesions (169).