Presentation of CaseA sixty-five-year-old woman entered the hospital because of weakness of the legs.Three weeks previously she noted the gradual onset of an ache in the lower portion of the back that subsided after three days. There was no history of trauma. Subsequently, there were persistent, crampy pains in the calves that were worse on the right side and an inability to climb stairs because of weakness of the legs that was worse on the left side. Coughing made the pain in the right leg worse. Numbness of the lateral aspect of the left calf and the left . . .