This sounds a viral infection more than a spinal cord problem.
New castle disease can be seen in chicken between the age of 1 week to 72 weeks .It is caused by a virus called paramyxo virus and is the most important and most prevalent disease in poultry.
Sudden death is common.With very harmful viruses, first indication is sudden death. Then, symptoms such as depression, weakness,
lying down, green diarrhea, swelling of the face, and nervous signs may appear, ending in exhaustion and
death. Other signs include twisting of the neck, paralysis of legs
and arched position of the body.
Mortality may occur up to 100% in chicks.
Marek's disease :Marek's disease affects chickens from about 4-6 weeks of age. It occurs usually between 12 and 24 weeks of age, but older birds may also be affected.A particularly characteristic posture is that in which the bird lies on its side with one leg stretched forward and the other backward
Non-specific signs such as weight loss, paleness, shrunken combs, loss of
appetite, and diarrhea may be observed, especially in birds in which the course is prolonged.
Unfortunately there is no known treatment for the viral diseases I mentioned above.
Please follow the link for more information about the Marek's disease.
I hope this helps. If you would like to ask more questions please come back and post here. I may not respond right away but will be reading my posts tomorrow.