Sensation begins with the nerves in our limbs. Nerve impulses travel to the spinal cord, the brain, and then to the cortex for conscious appreciation. There are many causes of disruption in this pathway. A common cause is diabetes; uncommon causes include exposure to heavy metals, such as mercury, arsenic, and lead, as well as remote effects of cancer. But these are all diseases that progress slowly; Susan’s disease was moving quickly. I knew of several possible causes, but only one was likely: chronic inflammatory demyelinating polyneuropathy, or CIDP.
CIDP is an autoimmune disease. For unknown reasons, the immune system sometimes produces antibodies that mistakenly attack the body’s own tissues. In CIDP, antibodies strip the sheath that surrounds the nerve fibers. The loss of myelin slows or blocks the conduction of nerve impulses and leads to symptoms; if motor nerves are involved, the patient will develop weakness, and if sensory nerves are involved, as in Susan’s case, the patient will experience numbness and loss of sensation.
The exact number of patients with CIDP is not known, but in the United States the number probably exceeds 100,000. The disease can affect people of all ages, but the peak incidence occurs in the fifth and sixth decades of life. Although it can have an impact on different people in different ways, and spontaneous remissions can occur, CIDP tends to be associated with prolonged neurological disability, with roughly 20 percent of patients being confined to a wheelchair or bed.
Once CIDP is suspected, diagnosis is not very difficult. Blood tests will exclude systemic disorders, such as diabetes, as a cause. Radiographs can reveal the structural integrity of the spinal cord, but the diagnostic gold standard is a test called NCV, for nerve conduction velocity. NCVs are performed by electrically stimulating a nerve and measuring how fast the impulse is conducted. In CIDP, the conduction velocities are markedly slowed, a finding consistent with demyelination.
CIDP can be treated, but there is no cure. Corticosteroids and other immunosuppressive agents are helpful in modulating the immune response. Two potent and widely accepted therapies include intravenous immunoglobulin, which helps the body rid itself of the auto- antibodies, and plasma exchange, a process that literally filters antibodies out of the plasma. These expensive therapies usually have no adverse side effects and may be used in tandem if one doesn’t work by itself, particularly in severe cases of CIDP. In many instances both therapies must be repeated regularly to keep the immune response under control.
Susan’s blood work and radiographs were normal. Her NCVs showed markedly prolonged conduction times, so I knew I had the correct diagnosis. Her numbness, however, was getting worse, and the disease began to affect the nerves that control movement as well.
I was concerned that side effects from steroids might be too much for Susan to handle at her age. We agreed to try the intravenous immunoglobulin first. She handled it well, but the benefit was minimal. I tried plasma exchange next, but she didn’t tolerate the procedure, and much worse, her symptoms didn’t improve.
I was running out of options, and Susan was desperate. I felt her despair and knew I had to move quickly. Often a repeat treatment works, so I returned to the intravenous immunoglobulin. This time it was successful. Her symptoms stopped getting worse, and after several treatments, she slowly started to improve.
Susan has been receiving immunoglobulin treatments regularly, and although she isn’t cured, she is stable. The last time I saw her, I knew I’d kept my promise. When she left my office, she walked down the hallway without assistance.
John Pettinato is a neurologist in Concord, New Hampshire. The cases described in Vital Signs are true stories, but the authors have changed some details about the patients to protect their privacy.