Disseminated or multiple sclerosis occurs in both the brain and the spinal cord, and is characterized in the early stage by the presence of many softened areas. These vary in size, are grayish in color, are more frequently found in the white matter than in the gray. There is a degeneration of the myelin and of the cells, but the axis-cylinders remain uninvolved for a long time. Hyaline degeneration of the blood-vessels is commonly present. As the disease progresses, the softened areas are gradually replaced by a hyperplasia of the glia tissue. There is also atrophy of the nerve-cells and of some of the axis-cylinders.

The etiology of this disease is obscure. It is found in syphilis, in acute infectious diseases, in chronic metallic poisoning, and in injuries.

Fig. 185. - Tabes Dorsalis (Collins).

Posterior sclerosis, tabes dorsalis, or locomotor ataxia, is a condition of sclerotic changes in the posterior sensory columns. The present opinion is that it is the result of primary disease of the posterior nerve-roots. This is thought by many to depend generally upon syphilitic infection, but it occurs in traumatism and possibly in some of the infectious fevers. The lumbar portion is more commonly affected than the dorsal, and lastly the cervical. The degeneration usually develops in the lumbar cord, in the posterior nerve-roots. In the dorsal region there are also two areas of degeneration in the column of Burdach; and in the cervical region, the chief involvement is in the columns of Goll.

There is atrophy of the nervous tissue, with increase of the neuroglia. The myelin sheaths break down and expose the axis-cylinders, which resist the degenerative processes longer than the other tissues.

In advanced cases there may be almost no normal nerve fibers in the posterior columns, they having been replaced by dense fibrous tissue.

The lesions may not only affect the cord and peripheral nerves, but also involve areas in the brain and in the optic, oculomotor, and trigeminal nerves.

There are also degenerations nearly always present of the sensory nerve-endings.

The main symptoms are girdle pains, loss of knee-jerk, Argyll-Robertson pupils, loss of sensation and tactile sense.

Friedreich's disease, or hereditary ataxia, is a variety of posterior sclerosis that usually begins about the seventh year, and involves several members of a family. There is a hypoplasia of the cord or the cerebellum, and sclerosis of the posterior columns of the cord. The fibers in the column of Goll and the greater part of those in the column of Burdach degenerate, and the cells in the column of Clark are involved at times. There is also some degeneration of the direct cerebellar tract and of the lateral pyramidal columns as well. The lesions are most marked in the lower part of the cord.

Acute anterior poliomyelitis is characterized by degeneration and sclerosis of the anterior horns of the gray matter of the spinal cord. It occurs chiefly in children about three years old, but at times affects adults.

The cause is unknown, but the process is that of an acute inflammation. It is apparently either infectious or toxic in its origin and is distributed by the blood-vessels. The disease usually begins rapidly, and is accompanied by chills and fever.

The lesions may be unilateral or bilateral, and are more common in the lumbar region. Early in the disease the blood-vessels of the anterior horns of the gray matter are 36 distended, and the perivascular lymph-spaces filled with round-cells. Small interstitial hemorrhages may be present in the anterior horns. The ganglion-cells become larger, granular, and cloudy, often vacuolated, and altered in their staining reactions. The cells eventually become completely degenerated and disappear, the medullated nerves lose their covering, and many are destroyed. Neurogliar hyperplasia occurs in the involved areas, and the gray matter may become much indurated.

Fig. 186. - Chronic Anterior Poliomyelitis (Collins).

Chronic anterior poliomyelitis or progressive muscular atrophy occurs generally in adults, and is characterized by atrophy and disappearance of the motor cells of the anterior horns of the spinal cord. The small muscles of the hand are the first to undergo atrophy, then those of the arms, shoulders, and body.

The diaphragm may become involved and death result. The change is one of fatty degeneration.

The lesions generally appear in the cervical and upper dorsal portions of the cord, and extend along the anterior cornua in both directions. When the medulla is affected, the resulting condition is known as bulbar palsy.

Bulbar palsy is similar to the above except that it occurs in the medulla instead of in the cord, and affects the ganglia of the hypoglossus, glossopharyngeal, spinal accessory, vagus, facial, abducens, and motor portion of the trigeminus.

Amyotrophic lateral sclerosis is a disease in which there is a degeneration of the peripheral motor nerves as well as an atrophy of the motor cells in the anterior horns of the gray matter of the cord. There is also more or less degeneration of the pyramidal columns. The muscles undergo the same changes as in progressive muscular atrophy.

Fig. 187. - Combined Posterior and Lateral Sclerosis (Collins).

The degenerations begin in the sacral and lumbar portions of the cord and extend upward.