A new type of inclusion body in human spinal cord.

New pericapillary inclusion bodies were found in 17 cases of sporadic amyotrophic lateral sclerosis (ALS). The inclusion bodies consisted of paracrystalline arrays with 5-7 nm electron-dense subunits, were discernible with the light microscope and had the staining properties of protein. They were surrounded by capillary-wall basement membrane and were often associated with peripheral fibrils. Astrocytic fibrillary bodies, without paracrystalline material, were also found. The ultrastructure and staining of the fibrils suggests that the paracrystalline material is within pericapillary astrocytes. The nature and significance of the inclusion bodies are unknown, but their presence suggests that there may be pericapillary abnormalities in the spinal cord in ALS and possibly other disorders.