The role of axonal transport in neurodegenerative disease spread: a meta-analysis of experimental and clinical poliomyelitis compares with amyotrophic lateral sclerosis.

ALS symptom spread results from local spread of the neuronal degeneration because contiguous areas are more quickly involved than non-contiguous areas. Local spread to contiguous areas of motor neuron dysfunction is faster at the brainstem, cervical and lumbar regions than spread to non-contiguous areas. The time for caudal-rostral symptomatic spread of ALS to involve a distant region is a function of the distance of that region from the site of onset. The time for spread to the bulbar region is shorter following arm onset than leg onset. Spread to non-contiguous areas is faster within the spinal cord than from the spinal cord to the bulbar region. These kinetics are consistent with axonal transport of the etiological agent in a manner similar to spread of poliovirus in poliomyelitis patients. Spread from the bulbar region to the spinal cord, on the other hand, occurs faster than symptom spread from the limb region to the bulbar region in limb onset patients. This rapid limb involvement following bulbar onset is more dramatic in males compared with females. Females with leg onset, on the other hand, show more rapid involvement of the opposite leg, either arm or bulbar structures than males. Gender effects may determine the course of ALS depending on the original site of onset.