Ubiquitinated dystrophic neurites suggest corticospinal derangement in patients with amyotrophic lateral sclerosis.

Pathologic changes affecting the upper motoneuron (UMN) were studied in 37 cases of amyotrophic lateral sclerosis (ALS) by histology and immunohistochemistry and by electron and immunoelectron microscopy. The most striking finding was represented by ubiquitin-positive dot-like structures related to (1) glial lipofuscin granules, (2) small polyglucosan bodies and (3) dystrophic neurites. Their distribution areas did not overlap. In ALS cases, ubiquitinated dystrophic neurites were twice as frequent as in controls in the arcuate region of motor cortex; moreover, in ALS cases they were twice as frequent in the spinal cord at the end of corticospinal tracts, compared with the motor cortex. These findings may indicate the presence in ALS of a 'dying-back' of the corticospinal motoneuron, independently of its primary or secondary involvement.