any deviation from a healthy or normal condition

become hard or harder

make hard or harder

a chronic progressive nervous disorder involving loss of myelin sheath around certain nerve fibers

thickening of tissue in the motor tracts of the lateral columns and anterior horns of the spinal cord; results in progressive muscle atrophy that starts in the limbs

sclerosis of the arterioles

sclerosis of the arterial walls

abnormal hardening or eburnation of bone