Increased number of astrocytes and macrophages/microglial cells in the corpus callosum in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by degeneration of both upper and lower motor neurons. Neuropathologically, degeneration of the corticospinal tracts is evident and may be associated with loss of motor neurons in the motor cortex. The data from a recently developed imaging technology, the diffusion tensor imaging method of MRI have suggested that white matter in the corpus callosum (CC) is lost in patients with ALS. However, the specific neuropathologic changes of the commissural fibers remain unclear. To investigate the pathologic changes of the CC in ALS, we analyzed midsagittal sections of the CC from eight individuals with ALS and eight controls by using conventional staining and immunohistochemistry with antibodies against CD68, GFAP and phosphorylated neurofilament (SMI‐31). The CC was divided into seven areas. The number of CD68‐immunoreactive macrophages/microglia and GFAP‐immunoreactive astrocytes was significantly higher in individuals with ALS than in controls in all areas of the CC except the rostrum. Among the patients with ALS, the number of macrophages/microglia and astrocytes was significantly higher in the posterior midbody and isthmus than in the rostrum. There was no significant difference in number of SMI‐31 immunoreactive axons between ALS and control group as well as among each area of the CC. These findings suggest that pathologic changes in the CC in ALS are present in the posterior midbody and isthmus, where callosal motor fibers may traverse between the two hemispheres. CD68 and GFAP immunohistochemistry are sensitive methods to detect those pathologic changes in routine paraffin‐embedded specimens.