Poliomyelitis

Poliomyelitis, or infantile paralysis, is an acute infective disease due to a virus with a predilection for the cells of the anterior horns of the grey matter of the spinal cord and the motor nuclei of the brain stem, destruction of which causes muscular paralysis and subsequent atrophy. Three strains of the virus have been isolated, known as Types 1, 2, and 3. These can be grown in tissue culture. The virus can be obtained from the nasopharyngeal mucous membranes of patients in the acute stage, of healthy contacts, and of convalescents, and also from the stools. It is believed that the usual route of infection in man is the alimentary tract. The neurotropism of the virus can be demonstrated by its inoculation into monkeys, usually into the spinal cord or brain. The virus is capable of ascending the peripheral nerves, but may also be disseminated through the blood stream.
  In the acute stage there is evidence of a general reaction to the infection, particularly in the lymphoid tissue, and the spinal cord is congested, soft, and oedematous.

Spinal Cord with Poliomyelitis

Histologically the changes in the nervous system are usually most marked in the grey matter of the spinal cord and medulla, wherethere is degeneration of the anterior horn cells and an inflammatory reaction with small haemorrhages in the grey matter. This consists of perivascular cuffing, mainly with lymphocytes, but with a smaller number of polymorphonuclear cells, and a diffuse infiltration of the grey matter with similar cells and cells of neuroglial origin. In some cases the brunt of the infection falls upon the brain stem. During recovery from the acute stage, ganglion cells which have not been too severely damaged may be restored to normal. Others disappear completely, so that sections show a paucity of cells in the anterior horns, with secondary degeneration in the corresponding anterior roots and peripheral nerves. The muscles supplied by these segments show varying degrees of neural atrophy.