If you have symptoms such as paralysis of limbs and loss of sensation, then a high cervical spinal cord lesion should be suspected. If symptoms are related ONLY to paralysis of the diaphragm, then I'd look for injury to the nerve after the fibers come out of the cord. Reading between the lines, I suspect that half the diaphragm is paralyzed, but I might be wrong. That too would suggest damage to the nerve rather than to the spinal cord. Don't forget that certain acute paralytic illnesses such as Guillain Barre SYndrome and Myasthenia Gravis can affect the diaphragm.
Botulism is another.
Once you have established the location of the lesion, then there are a whole bunch of questions to be considered. Consider tumors pressing on or invading the nerve to the diaphragm. Generally, we're looking for something mechanical. If you or someone you know really has this problem, I assume by now that you have seen a doctor. Thanks for your patience in waiting for your reply.