In 1875 Erb described a condition characterized clinically by paresis and spasm or rigidity in the inferior extremities, and without loss or impairment of sensation, and expressed the opinion that this depended on a primary degenerative change in the pyramidal fibres of the lateral columns of the cord. Since then this condition has been very frequently observed clinically, and has been the subject of much discussion. For a long time no indubitable anatomical evidence was forthcoming in support of the view advanced by Erb, and indeed, even now were we to confine ourselves to such cases occurring in the adult, the anatomical evidence is exceedingly meagre, nor has an absolutely conclusive demonstration of the condition been furnished. Still a case published by Dreschfeld in 1881 and another by Striimpell in 1894 almost satisfy the conditions. Although not infrequently observed clinically it is only rarely that such cases come to post-mortem examination, since the disease does not tend much to shorten life; and for long such autopsies as were obtained where the diagnosis of this condition had been made during life, gave no confirmation of its separate existence, but merely showed this condition to be part of, it might be, a disseminated sclerosis or a secondary degenerative change in the course of some form of myelitis. Westphal and some others have found a state of things which almost satisfies the conditions in some cases of paretic dementia.

The symptoms already referred to as characteristic of descending sclerosis are here very pronounced, namely, spasm of the muscles, chiefly of the lower extremities, with exaggerated tendon reflex. There is also, of course, paralysis.

The sclerosis is alleged to be primary or spontaneous and implicates both pyramidal tracts, having thus a distribution like that in the descending degenerations already described; but here it usually begins in the lumbar region of the cord, and both lateral tracts are simultaneously attacked. Occasionally there is an associated degeneration of the cells of the anterior cornua, and in that case there is muscular atrophy in addition to the other phenomena. To conditions of this kind, Charcot has given the name Amyotrophic lateral sclerosis.