Microglia
Research has discovered dystrophic (defective development) human microglia. "These cells are characterized by abnormalities in their cytoplasmic structure, such as deramified, atrophic, fragmented or unusually tortuous processes, frequently bearing spheroidal or bulbous swellings." The incidence of dystrophic microglia increases with aging. Microglial degeneration and death have been reported in research on Prion disease, Schizophrenia and Alzheimer's disease, indicating that microglial deterioration might be involved in neurodegenerative diseases. A complication of this theory is the fact that it is difficult to distinguish between "activated" and "dystrophic" microglia in the human brain.
Microglia
Microglial cells are extremely plastic, and undergo a variety of structural changes based on location and system needs. This level of plasticity is required to fulfill the vast variety of functions that microglia perform. The ability to transform distinguishes microglia from macrophages, which must be replaced on a regular basis, and provides them the ability to defend the CNS on extremely short notice without causing immunological disturbance. Microglia adopt a specific form, or phenotype, in response to the local conditions and chemical signals they have detected.