Phagocytized corpora amylacea as a histological hallmark of astrocytic injury in neuromyelitis optica

Abstract

Neuromyelitis optica (NMO) is an inflammatory demyelinating and necrotizing disorder of the CNS that mainly affects the optic nerve and spinal cord. The etiology is still uncertain; however, the discovery of serum anti-aquaporin-4 (AQP4) autoantibody is becoming the center of attention, and a new hypothesis is emerging that NMO is essentially astrocytopathy provoked by this autoantibody. In this study, we focused on corpora amylacea (CA), glycoproteinaceous inclusions in astrocytic processes. We examined 57 lesions in nine cases of NMO spectrum disorder, and demonstrated that CA were phagocytized by macrophages in 42 lesions (74%) of eight cases, while phagocytized figures were not seen in unaffected areas. Phagocytized CA were frequently encountered in early-phase lesions still retaining myelin structures, while fewer or none were found in chronic destructive lesions. Moreover, phagocytized CA were significantly smaller in diameter than intact ones, and CA were decreased or absent in most lesions assessed. These findings suggest the following pathophysiological process: the astrocytes are affected at an early phase in NMO, CA are expelled from the astrocytes and phagocytized by macrophages finally leading to clearance. A phagocytized figure and subsequent loss of CA can be a histological hallmark of astrocytic injury of NMO.