Syphilis is assigned as the cause of this disease in a large proportion of cases (according to Gowers in about two-thirds, and according to Erb even a larger proportion). Syphilis does not act by means of the local effects of a gumma or other inflammatory lesion. It seems rather that the disease is a remote effect of the syphilitic poison acting on a predisposed organ. In this respect it may perhaps be compared with amyloid degeneration, which is also a late result, on particular structures, of the syphilitic poison. The disease also occurs as a result of alcoholic excess, in which, again, the prolonged action of a poison is recognizable. Concussion of the spine, over-exertion, etc., have also been stated as causes.
In connection with the causes assigned, the fact should be borne in mind that the lesions are largely degenerative, but that they also partake of the characters of chronic inflammation. They may be compared with those in peripheral neuritis, which is due to the action of similar poisonous agents.
If the cord is examined in well-advanced cases of this disease, the Posterior white columns are found grey and shrunken, and the posterior roots are also atrophied. There is often meningitis, the soft membranes being thickened and adherent to the cord beneath and sometimes to the dura mater on the surface. In early stages of the disease the changes in the cord may be invisible to the naked eye, but can be detected with the microscope. In advanced stages there may be similar changes in the optic nerve, the oculo-motor, the hypoglossal, etc.
The minute changes consist in atrophy of the nerve fibres and increase of the connective tissue, similar to that described as occurring in secondary degenerations. As to the degree in which actual inflammatory processes exist opinions differ. The result is a sclerosis of the affected regions, and the tissue may have many amyloid bodies in it. These are round or oval bodies three or four times the size of blood-corpuscles, and presenting a peculiar bright glancing appearance (Fig. 314). They frequently present a concentric striation like grains of potato starch, and with iodine they take on a deep brown coloration. These bodies are sometimes present in such numbers as to form the most prominent feature under the microscope.
The posterior columns are the parts affected, but the disease does not invade these columns uniformly. Its special seat is the outer parts of the posterior columns, namely, the Posterior root-zones, or columns of Burdach, and it is stated that these alone are affected in the earlier stages (see Fig. 315). The Columns of G-oll are secondarily invaded, as the result of an ascending sclerosis. That this is so appears from the actual examination of the cord at various levels. The disease begins, and is usually most advanced, in the lumbar region, but in the lowest part of that region the lateral parts of the posterior columns may be alone involved. On passing upwards the columns of Goll become also affected, so that in the upper half of the lumbar swelling the degeneration may be co-extensive with the posterior columns. This continues in the dorsal region, but in the cervical the sclerosis begins to diminish externally, and shades off into the columns of Goll, in which it may be continued up into the restiform body. The actual primary lesion is therefore that in the external parts of the posterior columns, and the affection in the columns of Goll is really an ascending secondary degeneration, these columns being, as already stated, the principal seat of ascending sclerosis. It is to be noted, however, that the direct cerebellar tract and the antero-lateral tracts are not affected.
Fig. 314. - Amyloid bodies from cord, x 300.
Fig. 315. - Cord in early stage of locomotor ataxia. The columns of Goll are unaffected, but the posterior root-zones are in a state of sclerosis.
Besides extending to . the columns of Goll, the disease commonly affects also the Posterior roots, which are often much atrophied. It may also extend to the Posterior grey cornua, in which case anaesthesia occurs, or to the Lateral columns, in which case paralysis ensues; or it may even pass through to the Anterior cornua, when muscular atrophy occurs in addition to paralysis. There is sometimes an extension to the Medulla oblongata, as evidenced by inco-ordination of the muscles of the eyeball and of those of speech.
In a large proportion of cases the Peripheral nerves are affected similarly to the posterior columns of the cord. There is atrophy of the nerve fibres with increase of the connective tissue. It is the -t'lisory nerves which are affected, and chiefly the fine filaments in the skin and joints, but probably the sensory fibres of the muscles also. The lesion diminishes on passing from the finer filaments to the larger stems. There are frequently similar changes in the Optic nerve and in the Ascending root of the fifth.