She had diabetes and high blood pressure. And she was seeing a hematologist for a dangerously low white-blood-cell count that still was not explained. None of that helped account for why she was so unsteady on her feet. Although her legs were weak, Ahmed thought that it was mostly her balance that kept her from walking. Balance is a function of the nervous system. Diabetes can damage the nerves of the legs and feet but rarely causes this degree of disability.

Some type of injury to the spinal cord could cause this loss of feeling and coordination. Had the narrow, bony tube that protects the spinal column been made even narrower by an overgrowth of bone? That kind of pressure on the nerves is a relatively common problem as people get older. Some cancers could do this as well. A wildly proliferating tumor will sometimes create proteins that attack nerve cells. And cancer could account for her low white-blood-cell count as well. Were the two symptoms linked? A deficiency of vitamin B12 could affect the nervous system and the production of white blood cells. And it was also common in people over 60. The patient remembered being bitten by a mosquito before her symptoms started. Could this be the West Nile virus? It often attacks the spinal cord, causing weakness that can be permanent.

Ahmed quickly came up with a plan. Blood tests would show if she had been exposed to the West Nile virus or if she was low on vitamin B12. He would also test her for a cancer of the blood that could affect both blood and bone. The M.R.I. could tell him if the spinal cord was damaged or if she had cancer.

After finishing his notes, Ahmed went to the radiology department to check out the M.R.I. of the patient’s upper body and spine. It was normal. There was no sign of a cancer in the chest, abdomen or pelvis, and no sign of any damage to the spinal cord.

Image Tubes of denture adhesive

The next morning, results of the blood tests began to roll in. The vitamin B12 level was normal. She had never been exposed to the West Nile virus. There was no evidence of any blood cancer, either. Ahmed saw that the neurologist had ordered some blood tests before sending the patient for the M.R.I. — tests that Ahmed said he would not have thought of running. Two were strikingly abnormal: she had almost no copper in her system; and her zinc level was through the roof — more than twice the normal amount. Ahmed was surprised. Could abnormalities in these minerals do all this? He hurried to a computer to read up.